From fe15d706cfc1cb321dbe2329b04b5ca185edff60 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 4 Jan 2012 13:30:33 -0800 Subject: rcu: Add lockdep-RCU checks for simple self-deadlock It is illegal to have a grace period within a same-flavor RCU read-side critical section, so this commit adds lockdep-RCU checks to splat when such abuse is encountered. This commit does not detect more elaborate RCU deadlock situations. These situations might be a job for lockdep enhancements. Signed-off-by: Paul E. McKenney --- kernel/rcutiny.c | 4 ++++ kernel/rcutiny_plugin.h | 5 +++++ kernel/rcutree.c | 8 ++++++++ kernel/rcutree_plugin.h | 4 ++++ kernel/srcu.c | 6 ++++++ 5 files changed, 27 insertions(+) (limited to 'kernel') diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c index 977296dca0a4..8e00d461911e 100644 --- a/kernel/rcutiny.c +++ b/kernel/rcutiny.c @@ -319,6 +319,10 @@ static void rcu_process_callbacks(struct softirq_action *unused) */ void synchronize_sched(void) { + rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) && + !lock_is_held(&rcu_lock_map) && + !lock_is_held(&rcu_sched_lock_map), + "Illegal synchronize_sched() in RCU read-side critical section"); cond_resched(); } EXPORT_SYMBOL_GPL(synchronize_sched); diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h index 9cb1ae4aabdd..4b905404a5bd 100644 --- a/kernel/rcutiny_plugin.h +++ b/kernel/rcutiny_plugin.h @@ -706,6 +706,11 @@ EXPORT_SYMBOL_GPL(call_rcu); */ void synchronize_rcu(void) { + rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) && + !lock_is_held(&rcu_lock_map) && + !lock_is_held(&rcu_sched_lock_map), + "Illegal synchronize_rcu() in RCU read-side critical section"); + #ifdef CONFIG_DEBUG_LOCK_ALLOC if (!rcu_scheduler_active) return; diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 6c4a6722abfd..3cf713a724c1 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1816,6 +1816,10 @@ EXPORT_SYMBOL_GPL(call_rcu_bh); */ void synchronize_sched(void) { + rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) && + !lock_is_held(&rcu_lock_map) && + !lock_is_held(&rcu_sched_lock_map), + "Illegal synchronize_sched() in RCU-sched read-side critical section"); if (rcu_blocking_is_gp()) return; wait_rcu_gp(call_rcu_sched); @@ -1833,6 +1837,10 @@ EXPORT_SYMBOL_GPL(synchronize_sched); */ void synchronize_rcu_bh(void) { + rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) && + !lock_is_held(&rcu_lock_map) && + !lock_is_held(&rcu_sched_lock_map), + "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section"); if (rcu_blocking_is_gp()) return; wait_rcu_gp(call_rcu_bh); diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 8bb35d73e1f9..3680b6b35bf3 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -688,6 +688,10 @@ EXPORT_SYMBOL_GPL(call_rcu); */ void synchronize_rcu(void) { + rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) && + !lock_is_held(&rcu_lock_map) && + !lock_is_held(&rcu_sched_lock_map), + "Illegal synchronize_rcu() in RCU read-side critical section"); if (!rcu_scheduler_active) return; wait_rcu_gp(call_rcu); diff --git a/kernel/srcu.c b/kernel/srcu.c index 0febf61e1aa3..3f99fa0e8ed3 100644 --- a/kernel/srcu.c +++ b/kernel/srcu.c @@ -172,6 +172,12 @@ static void __synchronize_srcu(struct srcu_struct *sp, void (*sync_func)(void)) { int idx; + rcu_lockdep_assert(!lock_is_held(&sp->dep_map) && + !lock_is_held(&rcu_bh_lock_map) && + !lock_is_held(&rcu_lock_map) && + !lock_is_held(&rcu_sched_lock_map), + "Illegal synchronize_srcu() in same-type SRCU (or RCU) read-side critical section"); + idx = sp->completed; mutex_lock(&sp->mutex); -- cgit v1.2.3 From 0bb7b59d6e2b8440cd7097097dd4bbfc4d76ed07 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 5 Jan 2012 14:44:39 -0800 Subject: rcu: Add diagnostic for misaligned rcu_head structures The push for energy efficiency will require that RCU tag rcu_head structures to indicate whether or not their invocation is time critical. This tagging is best carried out in the bottom bits of the ->next pointers in the rcu_head structures. This tagging requires that the rcu_head structures be properly aligned, so this commit adds the required diagnostics. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 1 + 1 file changed, 1 insertion(+) (limited to 'kernel') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 3cf713a724c1..570f7530f4b3 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1707,6 +1707,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), unsigned long flags; struct rcu_data *rdp; + WARN_ON_ONCE((unsigned long)head & 0x3); /* Misaligned rcu_head! */ debug_rcu_head_queue(head); head->func = func; head->next = NULL; -- cgit v1.2.3 From 486e259340fc4c60474f2c14703e3b3634bb58ca Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 6 Jan 2012 14:11:30 -0800 Subject: rcu: Avoid waking up CPUs having only kfree_rcu() callbacks When CONFIG_RCU_FAST_NO_HZ is enabled, RCU will allow a given CPU to enter dyntick-idle mode even if it still has RCU callbacks queued. RCU avoids system hangs in this case by scheduling a timer for several jiffies in the future. However, if all of the callbacks on that CPU are from kfree_rcu(), there is no reason to wake the CPU up, as it is not a problem to defer freeing of memory. This commit therefore tracks the number of callbacks on a given CPU that are from kfree_rcu(), and avoids scheduling the timer if all of a given CPU's callbacks are from kfree_rcu(). Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- include/linux/rcupdate.h | 2 +- include/linux/rcutiny.h | 6 ++++ include/linux/rcutree.h | 2 ++ include/trace/events/rcu.h | 63 ++++++++++++++++++++++-------------- kernel/rcu.h | 4 ++- kernel/rcutiny.c | 4 +-- kernel/rcutree.c | 29 ++++++++++------- kernel/rcutree.h | 3 +- kernel/rcutree_plugin.h | 79 ++++++++++++++++++++++++++++++++++++++++++++-- kernel/rcutree_trace.c | 8 ++--- 10 files changed, 153 insertions(+), 47 deletions(-) (limited to 'kernel') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 81c04f4348ec..a67d5f1072ea 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -841,7 +841,7 @@ void __kfree_rcu(struct rcu_head *head, unsigned long offset) /* See the kfree_rcu() header comment. */ BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); - call_rcu(head, (rcu_callback)offset); + kfree_call_rcu(head, (rcu_callback)offset); } /** diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index 00b7a5e493d2..51bf29c81485 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -83,6 +83,12 @@ static inline void synchronize_sched_expedited(void) synchronize_sched(); } +static inline void kfree_call_rcu(struct rcu_head *head, + void (*func)(struct rcu_head *rcu)) +{ + call_rcu(head, func); +} + #ifdef CONFIG_TINY_RCU static inline void rcu_preempt_note_context_switch(void) diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index 73e7195f9997..73892483fd05 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -61,6 +61,8 @@ extern void synchronize_rcu_bh(void); extern void synchronize_sched_expedited(void); extern void synchronize_rcu_expedited(void); +void kfree_call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)); + static inline void synchronize_rcu_bh_expedited(void) { synchronize_sched_expedited(); diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h index d2d88bed891b..337099783f37 100644 --- a/include/trace/events/rcu.h +++ b/include/trace/events/rcu.h @@ -313,19 +313,22 @@ TRACE_EVENT(rcu_prep_idle, /* * Tracepoint for the registration of a single RCU callback function. * The first argument is the type of RCU, the second argument is - * a pointer to the RCU callback itself, and the third element is the - * new RCU callback queue length for the current CPU. + * a pointer to the RCU callback itself, the third element is the + * number of lazy callbacks queued, and the fourth element is the + * total number of callbacks queued. */ TRACE_EVENT(rcu_callback, - TP_PROTO(char *rcuname, struct rcu_head *rhp, long qlen), + TP_PROTO(char *rcuname, struct rcu_head *rhp, long qlen_lazy, + long qlen), - TP_ARGS(rcuname, rhp, qlen), + TP_ARGS(rcuname, rhp, qlen_lazy, qlen), TP_STRUCT__entry( __field(char *, rcuname) __field(void *, rhp) __field(void *, func) + __field(long, qlen_lazy) __field(long, qlen) ), @@ -333,11 +336,13 @@ TRACE_EVENT(rcu_callback, __entry->rcuname = rcuname; __entry->rhp = rhp; __entry->func = rhp->func; + __entry->qlen_lazy = qlen_lazy; __entry->qlen = qlen; ), - TP_printk("%s rhp=%p func=%pf %ld", - __entry->rcuname, __entry->rhp, __entry->func, __entry->qlen) + TP_printk("%s rhp=%p func=%pf %ld/%ld", + __entry->rcuname, __entry->rhp, __entry->func, + __entry->qlen_lazy, __entry->qlen) ); /* @@ -345,20 +350,21 @@ TRACE_EVENT(rcu_callback, * kfree() form. The first argument is the RCU type, the second argument * is a pointer to the RCU callback, the third argument is the offset * of the callback within the enclosing RCU-protected data structure, - * and the fourth argument is the new RCU callback queue length for the - * current CPU. + * the fourth argument is the number of lazy callbacks queued, and the + * fifth argument is the total number of callbacks queued. */ TRACE_EVENT(rcu_kfree_callback, TP_PROTO(char *rcuname, struct rcu_head *rhp, unsigned long offset, - long qlen), + long qlen_lazy, long qlen), - TP_ARGS(rcuname, rhp, offset, qlen), + TP_ARGS(rcuname, rhp, offset, qlen_lazy, qlen), TP_STRUCT__entry( __field(char *, rcuname) __field(void *, rhp) __field(unsigned long, offset) + __field(long, qlen_lazy) __field(long, qlen) ), @@ -366,41 +372,45 @@ TRACE_EVENT(rcu_kfree_callback, __entry->rcuname = rcuname; __entry->rhp = rhp; __entry->offset = offset; + __entry->qlen_lazy = qlen_lazy; __entry->qlen = qlen; ), - TP_printk("%s rhp=%p func=%ld %ld", + TP_printk("%s rhp=%p func=%ld %ld/%ld", __entry->rcuname, __entry->rhp, __entry->offset, - __entry->qlen) + __entry->qlen_lazy, __entry->qlen) ); /* * Tracepoint for marking the beginning rcu_do_batch, performed to start * RCU callback invocation. The first argument is the RCU flavor, - * the second is the total number of callbacks (including those that - * are not yet ready to be invoked), and the third argument is the - * current RCU-callback batch limit. + * the second is the number of lazy callbacks queued, the third is + * the total number of callbacks queued, and the fourth argument is + * the current RCU-callback batch limit. */ TRACE_EVENT(rcu_batch_start, - TP_PROTO(char *rcuname, long qlen, int blimit), + TP_PROTO(char *rcuname, long qlen_lazy, long qlen, int blimit), - TP_ARGS(rcuname, qlen, blimit), + TP_ARGS(rcuname, qlen_lazy, qlen, blimit), TP_STRUCT__entry( __field(char *, rcuname) + __field(long, qlen_lazy) __field(long, qlen) __field(int, blimit) ), TP_fast_assign( __entry->rcuname = rcuname; + __entry->qlen_lazy = qlen_lazy; __entry->qlen = qlen; __entry->blimit = blimit; ), - TP_printk("%s CBs=%ld bl=%d", - __entry->rcuname, __entry->qlen, __entry->blimit) + TP_printk("%s CBs=%ld/%ld bl=%d", + __entry->rcuname, __entry->qlen_lazy, __entry->qlen, + __entry->blimit) ); /* @@ -531,16 +541,21 @@ TRACE_EVENT(rcu_torture_read, #else /* #ifdef CONFIG_RCU_TRACE */ #define trace_rcu_grace_period(rcuname, gpnum, gpevent) do { } while (0) -#define trace_rcu_grace_period_init(rcuname, gpnum, level, grplo, grphi, qsmask) do { } while (0) +#define trace_rcu_grace_period_init(rcuname, gpnum, level, grplo, grphi, \ + qsmask) do { } while (0) #define trace_rcu_preempt_task(rcuname, pid, gpnum) do { } while (0) #define trace_rcu_unlock_preempted_task(rcuname, gpnum, pid) do { } while (0) -#define trace_rcu_quiescent_state_report(rcuname, gpnum, mask, qsmask, level, grplo, grphi, gp_tasks) do { } while (0) +#define trace_rcu_quiescent_state_report(rcuname, gpnum, mask, qsmask, level, \ + grplo, grphi, gp_tasks) do { } \ + while (0) #define trace_rcu_fqs(rcuname, gpnum, cpu, qsevent) do { } while (0) #define trace_rcu_dyntick(polarity, oldnesting, newnesting) do { } while (0) #define trace_rcu_prep_idle(reason) do { } while (0) -#define trace_rcu_callback(rcuname, rhp, qlen) do { } while (0) -#define trace_rcu_kfree_callback(rcuname, rhp, offset, qlen) do { } while (0) -#define trace_rcu_batch_start(rcuname, qlen, blimit) do { } while (0) +#define trace_rcu_callback(rcuname, rhp, qlen_lazy, qlen) do { } while (0) +#define trace_rcu_kfree_callback(rcuname, rhp, offset, qlen_lazy, qlen) \ + do { } while (0) +#define trace_rcu_batch_start(rcuname, qlen_lazy, qlen, blimit) \ + do { } while (0) #define trace_rcu_invoke_callback(rcuname, rhp) do { } while (0) #define trace_rcu_invoke_kfree_callback(rcuname, rhp, offset) do { } while (0) #define trace_rcu_batch_end(rcuname, callbacks_invoked, cb, nr, iit, risk) \ diff --git a/kernel/rcu.h b/kernel/rcu.h index aa88baab5f78..a074b0b43fc2 100644 --- a/kernel/rcu.h +++ b/kernel/rcu.h @@ -76,16 +76,18 @@ static inline void debug_rcu_head_unqueue(struct rcu_head *head) extern void kfree(const void *); -static inline void __rcu_reclaim(char *rn, struct rcu_head *head) +static inline bool __rcu_reclaim(char *rn, struct rcu_head *head) { unsigned long offset = (unsigned long)head->func; if (__is_kfree_rcu_offset(offset)) { RCU_TRACE(trace_rcu_invoke_kfree_callback(rn, head, offset)); kfree((void *)head - offset); + return 1; } else { RCU_TRACE(trace_rcu_invoke_callback(rn, head)); head->func(head); + return 0; } } diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c index 8e00d461911e..4eb34fcc2a75 100644 --- a/kernel/rcutiny.c +++ b/kernel/rcutiny.c @@ -258,7 +258,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp) /* If no RCU callbacks ready to invoke, just return. */ if (&rcp->rcucblist == rcp->donetail) { - RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1)); + RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, 0, -1)); RCU_TRACE(trace_rcu_batch_end(rcp->name, 0, ACCESS_ONCE(rcp->rcucblist), need_resched(), @@ -269,7 +269,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp) /* Move the ready-to-invoke callbacks to a local list. */ local_irq_save(flags); - RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1)); + RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1)); list = rcp->rcucblist; rcp->rcucblist = *rcp->donetail; *rcp->donetail = NULL; diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 570f7530f4b3..acf2d67ad2f4 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1261,6 +1261,7 @@ static void rcu_send_cbs_to_online(struct rcu_state *rsp) *receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist; receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL]; + receive_rdp->qlen_lazy += rdp->qlen_lazy; receive_rdp->qlen += rdp->qlen; receive_rdp->n_cbs_adopted += rdp->qlen; rdp->n_cbs_orphaned += rdp->qlen; @@ -1268,6 +1269,7 @@ static void rcu_send_cbs_to_online(struct rcu_state *rsp) rdp->nxtlist = NULL; for (i = 0; i < RCU_NEXT_SIZE; i++) rdp->nxttail[i] = &rdp->nxtlist; + rdp->qlen_lazy = 0; rdp->qlen = 0; } @@ -1368,11 +1370,11 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp) { unsigned long flags; struct rcu_head *next, *list, **tail; - int bl, count; + int bl, count, count_lazy; /* If no callbacks are ready, just return.*/ if (!cpu_has_callbacks_ready_to_invoke(rdp)) { - trace_rcu_batch_start(rsp->name, 0, 0); + trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0); trace_rcu_batch_end(rsp->name, 0, !!ACCESS_ONCE(rdp->nxtlist), need_resched(), is_idle_task(current), rcu_is_callbacks_kthread()); @@ -1385,7 +1387,7 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp) */ local_irq_save(flags); bl = rdp->blimit; - trace_rcu_batch_start(rsp->name, rdp->qlen, bl); + trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl); list = rdp->nxtlist; rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL]; *rdp->nxttail[RCU_DONE_TAIL] = NULL; @@ -1396,12 +1398,13 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp) local_irq_restore(flags); /* Invoke callbacks. */ - count = 0; + count = count_lazy = 0; while (list) { next = list->next; prefetch(next); debug_rcu_head_unqueue(list); - __rcu_reclaim(rsp->name, list); + if (__rcu_reclaim(rsp->name, list)) + count_lazy++; list = next; /* Stop only if limit reached and CPU has something to do. */ if (++count >= bl && @@ -1416,6 +1419,7 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp) rcu_is_callbacks_kthread()); /* Update count, and requeue any remaining callbacks. */ + rdp->qlen_lazy -= count_lazy; rdp->qlen -= count; rdp->n_cbs_invoked += count; if (list != NULL) { @@ -1702,7 +1706,7 @@ static void invoke_rcu_core(void) static void __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), - struct rcu_state *rsp) + struct rcu_state *rsp, bool lazy) { unsigned long flags; struct rcu_data *rdp; @@ -1727,12 +1731,14 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), *rdp->nxttail[RCU_NEXT_TAIL] = head; rdp->nxttail[RCU_NEXT_TAIL] = &head->next; rdp->qlen++; + if (lazy) + rdp->qlen_lazy++; if (__is_kfree_rcu_offset((unsigned long)func)) trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func, - rdp->qlen); + rdp->qlen_lazy, rdp->qlen); else - trace_rcu_callback(rsp->name, head, rdp->qlen); + trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen); /* If interrupts were disabled, don't dive into RCU core. */ if (irqs_disabled_flags(flags)) { @@ -1779,16 +1785,16 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), */ void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) { - __call_rcu(head, func, &rcu_sched_state); + __call_rcu(head, func, &rcu_sched_state, 0); } EXPORT_SYMBOL_GPL(call_rcu_sched); /* - * Queue an RCU for invocation after a quicker grace period. + * Queue an RCU callback for invocation after a quicker grace period. */ void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) { - __call_rcu(head, func, &rcu_bh_state); + __call_rcu(head, func, &rcu_bh_state, 0); } EXPORT_SYMBOL_GPL(call_rcu_bh); @@ -2036,6 +2042,7 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp) rdp->nxtlist = NULL; for (i = 0; i < RCU_NEXT_SIZE; i++) rdp->nxttail[i] = &rdp->nxtlist; + rdp->qlen_lazy = 0; rdp->qlen = 0; rdp->dynticks = &per_cpu(rcu_dynticks, cpu); WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_NESTING); diff --git a/kernel/rcutree.h b/kernel/rcutree.h index fddff92d6676..af2af3cc5e65 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -265,7 +265,8 @@ struct rcu_data { */ struct rcu_head *nxtlist; struct rcu_head **nxttail[RCU_NEXT_SIZE]; - long qlen; /* # of queued callbacks */ + long qlen_lazy; /* # of lazy queued callbacks */ + long qlen; /* # of queued callbacks, incl lazy */ long qlen_last_fqs_check; /* qlen at last check for QS forcing */ unsigned long n_cbs_invoked; /* count of RCU cbs invoked. */ diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 3680b6b35bf3..7adf232bb66b 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -671,10 +671,24 @@ static void rcu_preempt_do_callbacks(void) */ void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) { - __call_rcu(head, func, &rcu_preempt_state); + __call_rcu(head, func, &rcu_preempt_state, 0); } EXPORT_SYMBOL_GPL(call_rcu); +/* + * Queue an RCU callback for lazy invocation after a grace period. + * This will likely be later named something like "call_rcu_lazy()", + * but this change will require some way of tagging the lazy RCU + * callbacks in the list of pending callbacks. Until then, this + * function may only be called from __kfree_rcu(). + */ +void kfree_call_rcu(struct rcu_head *head, + void (*func)(struct rcu_head *rcu)) +{ + __call_rcu(head, func, &rcu_preempt_state, 1); +} +EXPORT_SYMBOL_GPL(kfree_call_rcu); + /** * synchronize_rcu - wait until a grace period has elapsed. * @@ -1064,6 +1078,22 @@ static void rcu_preempt_process_callbacks(void) { } +/* + * Queue an RCU callback for lazy invocation after a grace period. + * This will likely be later named something like "call_rcu_lazy()", + * but this change will require some way of tagging the lazy RCU + * callbacks in the list of pending callbacks. Until then, this + * function may only be called from __kfree_rcu(). + * + * Because there is no preemptible RCU, we use RCU-sched instead. + */ +void kfree_call_rcu(struct rcu_head *head, + void (*func)(struct rcu_head *rcu)) +{ + __call_rcu(head, func, &rcu_sched_state, 1); +} +EXPORT_SYMBOL_GPL(kfree_call_rcu); + /* * Wait for an rcu-preempt grace period, but make it happen quickly. * But because preemptible RCU does not exist, map to rcu-sched. @@ -2051,6 +2081,48 @@ int rcu_needs_cpu(int cpu) return per_cpu(rcu_dyntick_holdoff, cpu) == jiffies; } +/* + * Does the specified flavor of RCU have non-lazy callbacks pending on + * the specified CPU? Both RCU flavor and CPU are specified by the + * rcu_data structure. + */ +static bool __rcu_cpu_has_nonlazy_callbacks(struct rcu_data *rdp) +{ + return rdp->qlen != rdp->qlen_lazy; +} + +#ifdef CONFIG_TREE_PREEMPT_RCU + +/* + * Are there non-lazy RCU-preempt callbacks? (There cannot be if there + * is no RCU-preempt in the kernel.) + */ +static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu) +{ + struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu); + + return __rcu_cpu_has_nonlazy_callbacks(rdp); +} + +#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ + +static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu) +{ + return 0; +} + +#endif /* else #ifdef CONFIG_TREE_PREEMPT_RCU */ + +/* + * Does any flavor of RCU have non-lazy callbacks on the specified CPU? + */ +static bool rcu_cpu_has_nonlazy_callbacks(int cpu) +{ + return __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_sched_data, cpu)) || + __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_bh_data, cpu)) || + rcu_preempt_cpu_has_nonlazy_callbacks(cpu); +} + /* * Timer handler used to force CPU to start pushing its remaining RCU * callbacks in the case where it entered dyntick-idle mode with callbacks @@ -2149,8 +2221,9 @@ static void rcu_prepare_for_idle(int cpu) trace_rcu_prep_idle("Dyntick with callbacks"); per_cpu(rcu_dyntick_drain, cpu) = 0; per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1; - hrtimer_start(&per_cpu(rcu_idle_gp_timer, cpu), - rcu_idle_gp_wait, HRTIMER_MODE_REL); + if (rcu_cpu_has_nonlazy_callbacks(cpu)) + hrtimer_start(&per_cpu(rcu_idle_gp_timer, cpu), + rcu_idle_gp_wait, HRTIMER_MODE_REL); return; /* Nothing more to do immediately. */ } else if (--per_cpu(rcu_dyntick_drain, cpu) <= 0) { /* We have hit the limit, so time to give up. */ diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c index 654cfe67f0d1..db0987c1e1bd 100644 --- a/kernel/rcutree_trace.c +++ b/kernel/rcutree_trace.c @@ -73,8 +73,8 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp) rdp->dynticks->dynticks_nmi_nesting, rdp->dynticks_fqs); seq_printf(m, " of=%lu ri=%lu", rdp->offline_fqs, rdp->resched_ipi); - seq_printf(m, " ql=%ld qs=%c%c%c%c", - rdp->qlen, + seq_printf(m, " ql=%ld/%ld qs=%c%c%c%c", + rdp->qlen_lazy, rdp->qlen, ".N"[rdp->nxttail[RCU_NEXT_READY_TAIL] != rdp->nxttail[RCU_NEXT_TAIL]], ".R"[rdp->nxttail[RCU_WAIT_TAIL] != @@ -145,7 +145,7 @@ static void print_one_rcu_data_csv(struct seq_file *m, struct rcu_data *rdp) rdp->dynticks->dynticks_nmi_nesting, rdp->dynticks_fqs); seq_printf(m, ",%lu,%lu", rdp->offline_fqs, rdp->resched_ipi); - seq_printf(m, ",%ld,\"%c%c%c%c\"", rdp->qlen, + seq_printf(m, ",%ld,%ld,\"%c%c%c%c\"", rdp->qlen_lazy, rdp->qlen, ".N"[rdp->nxttail[RCU_NEXT_READY_TAIL] != rdp->nxttail[RCU_NEXT_TAIL]], ".R"[rdp->nxttail[RCU_WAIT_TAIL] != @@ -168,7 +168,7 @@ static int show_rcudata_csv(struct seq_file *m, void *unused) { seq_puts(m, "\"CPU\",\"Online?\",\"c\",\"g\",\"pq\",\"pgp\",\"pq\","); seq_puts(m, "\"dt\",\"dt nesting\",\"dt NMI nesting\",\"df\","); - seq_puts(m, "\"of\",\"ri\",\"ql\",\"qs\""); + seq_puts(m, "\"of\",\"ri\",\"qll\",\"ql\",\"qs\""); #ifdef CONFIG_RCU_BOOST seq_puts(m, "\"kt\",\"ktl\""); #endif /* #ifdef CONFIG_RCU_BOOST */ -- cgit v1.2.3 From e5601400081651060a59bd1f45f2821bb8e97f95 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sat, 7 Jan 2012 11:03:57 -0800 Subject: rcu: Simplify offline processing Move ->qsmaskinit and blkd_tasks[] manipulation to the CPU_DYING notifier. This simplifies the code by eliminating a potential deadlock and by reducing the responsibilities of force_quiescent_state(). Also rename functions to make their connection to the CPU-hotplug stages explicit. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 160 +++++++++++++++++++++++------------------------- kernel/rcutree.h | 4 +- kernel/rcutree_plugin.h | 25 ++++---- 3 files changed, 90 insertions(+), 99 deletions(-) (limited to 'kernel') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index acf2d67ad2f4..575f91d03f06 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -943,6 +943,10 @@ rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_dat * in preparation for detecting the next grace period. The caller must hold * the root node's ->lock, which is released before return. Hard irqs must * be disabled. + * + * Note that it is legal for a dying CPU (which is marked as offline) to + * invoke this function. This can happen when the dying CPU reports its + * quiescent state. */ static void rcu_start_gp(struct rcu_state *rsp, unsigned long flags) @@ -1245,118 +1249,101 @@ rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp) /* * Move a dying CPU's RCU callbacks to online CPU's callback list. - * Synchronization is not required because this function executes - * in stop_machine() context. + * Also record a quiescent state for this CPU for the current grace period. + * Synchronization and interrupt disabling are not required because + * this function executes in stop_machine() context. Therefore, cleanup + * operations that might block must be done later from the CPU_DEAD + * notifier. + * + * Note that the outgoing CPU's bit has already been cleared in the + * cpu_online_mask. This allows us to randomly pick a callback + * destination from the bits set in that mask. */ -static void rcu_send_cbs_to_online(struct rcu_state *rsp) +static void rcu_cleanup_dying_cpu(struct rcu_state *rsp) { + unsigned long flags; int i; - /* current DYING CPU is cleared in the cpu_online_mask */ + unsigned long mask; + int need_report; int receive_cpu = cpumask_any(cpu_online_mask); struct rcu_data *rdp = this_cpu_ptr(rsp->rda); struct rcu_data *receive_rdp = per_cpu_ptr(rsp->rda, receive_cpu); + struct rcu_node *rnp = rdp->mynode; /* For dying CPU. */ + + /* Move callbacks to some other CPU. */ + if (rdp->nxtlist != NULL) { + *receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist; + receive_rdp->nxttail[RCU_NEXT_TAIL] = + rdp->nxttail[RCU_NEXT_TAIL]; + receive_rdp->qlen_lazy += rdp->qlen_lazy; + receive_rdp->qlen += rdp->qlen; + receive_rdp->n_cbs_adopted += rdp->qlen; + rdp->n_cbs_orphaned += rdp->qlen; + + rdp->nxtlist = NULL; + for (i = 0; i < RCU_NEXT_SIZE; i++) + rdp->nxttail[i] = &rdp->nxtlist; + rdp->qlen_lazy = 0; + rdp->qlen = 0; + } - if (rdp->nxtlist == NULL) - return; /* irqs disabled, so comparison is stable. */ - - *receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist; - receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL]; - receive_rdp->qlen_lazy += rdp->qlen_lazy; - receive_rdp->qlen += rdp->qlen; - receive_rdp->n_cbs_adopted += rdp->qlen; - rdp->n_cbs_orphaned += rdp->qlen; - - rdp->nxtlist = NULL; - for (i = 0; i < RCU_NEXT_SIZE; i++) - rdp->nxttail[i] = &rdp->nxtlist; - rdp->qlen_lazy = 0; - rdp->qlen = 0; -} - -/* - * Remove the outgoing CPU from the bitmasks in the rcu_node hierarchy - * and move all callbacks from the outgoing CPU to the current one. - * There can only be one CPU hotplug operation at a time, so no other - * CPU can be attempting to update rcu_cpu_kthread_task. - */ -static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp) -{ - unsigned long flags; - unsigned long mask; - int need_report = 0; - struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); - struct rcu_node *rnp; - - rcu_stop_cpu_kthread(cpu); - - /* Exclude any attempts to start a new grace period. */ - raw_spin_lock_irqsave(&rsp->onofflock, flags); - - /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */ - rnp = rdp->mynode; /* this is the outgoing CPU's rnp. */ + /* Record a quiescent state for the dying CPU. */ mask = rdp->grpmask; /* rnp->grplo is constant. */ + trace_rcu_grace_period(rsp->name, + rnp->gpnum + 1 - !!(rnp->qsmask & mask), + "cpuofl"); + rcu_report_qs_rdp(smp_processor_id(), rsp, rdp, rsp->gpnum); + /* Note that rcu_report_qs_rdp() might call trace_rcu_grace_period(). */ + + /* + * Remove the dying CPU from the bitmasks in the rcu_node + * hierarchy. Because we are in stop_machine() context, we + * automatically exclude ->onofflock critical sections. + */ do { - raw_spin_lock(&rnp->lock); /* irqs already disabled. */ + raw_spin_lock_irqsave(&rnp->lock, flags); rnp->qsmaskinit &= ~mask; if (rnp->qsmaskinit != 0) { - if (rnp != rdp->mynode) - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ - else - trace_rcu_grace_period(rsp->name, - rnp->gpnum + 1 - - !!(rnp->qsmask & mask), - "cpuofl"); + raw_spin_unlock_irqrestore(&rnp->lock, flags); break; } if (rnp == rdp->mynode) { - trace_rcu_grace_period(rsp->name, - rnp->gpnum + 1 - - !!(rnp->qsmask & mask), - "cpuofl"); need_report = rcu_preempt_offline_tasks(rsp, rnp, rdp); + if (need_report & RCU_OFL_TASKS_NORM_GP) + rcu_report_unblock_qs_rnp(rnp, flags); + else + raw_spin_unlock_irqrestore(&rnp->lock, flags); + if (need_report & RCU_OFL_TASKS_EXP_GP) + rcu_report_exp_rnp(rsp, rnp, true); } else - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ + raw_spin_unlock_irqrestore(&rnp->lock, flags); mask = rnp->grpmask; rnp = rnp->parent; } while (rnp != NULL); - - /* - * We still hold the leaf rcu_node structure lock here, and - * irqs are still disabled. The reason for this subterfuge is - * because invoking rcu_report_unblock_qs_rnp() with ->onofflock - * held leads to deadlock. - */ - raw_spin_unlock(&rsp->onofflock); /* irqs remain disabled. */ - rnp = rdp->mynode; - if (need_report & RCU_OFL_TASKS_NORM_GP) - rcu_report_unblock_qs_rnp(rnp, flags); - else - raw_spin_unlock_irqrestore(&rnp->lock, flags); - if (need_report & RCU_OFL_TASKS_EXP_GP) - rcu_report_exp_rnp(rsp, rnp, true); - rcu_node_kthread_setaffinity(rnp, -1); } /* - * Remove the specified CPU from the RCU hierarchy and move any pending - * callbacks that it might have to the current CPU. This code assumes - * that at least one CPU in the system will remain running at all times. - * Any attempt to offline -all- CPUs is likely to strand RCU callbacks. + * The CPU has been completely removed, and some other CPU is reporting + * this fact from process context. Do the remainder of the cleanup. + * There can only be one CPU hotplug operation at a time, so no other + * CPU can be attempting to update rcu_cpu_kthread_task. */ -static void rcu_offline_cpu(int cpu) +static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp) { - __rcu_offline_cpu(cpu, &rcu_sched_state); - __rcu_offline_cpu(cpu, &rcu_bh_state); - rcu_preempt_offline_cpu(cpu); + struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); + struct rcu_node *rnp = rdp->mynode; + + rcu_stop_cpu_kthread(cpu); + rcu_node_kthread_setaffinity(rnp, -1); } #else /* #ifdef CONFIG_HOTPLUG_CPU */ -static void rcu_send_cbs_to_online(struct rcu_state *rsp) +static void rcu_cleanup_dying_cpu(struct rcu_state *rsp) { } -static void rcu_offline_cpu(int cpu) +static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp) { } @@ -1725,6 +1712,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), * a quiescent state betweentimes. */ local_irq_save(flags); + WARN_ON_ONCE(cpu_is_offline(smp_processor_id())); rdp = this_cpu_ptr(rsp->rda); /* Add the callback to our list. */ @@ -2155,16 +2143,18 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self, * touch any data without introducing corruption. We send the * dying CPU's callbacks to an arbitrarily chosen online CPU. */ - rcu_send_cbs_to_online(&rcu_bh_state); - rcu_send_cbs_to_online(&rcu_sched_state); - rcu_preempt_send_cbs_to_online(); + rcu_cleanup_dying_cpu(&rcu_bh_state); + rcu_cleanup_dying_cpu(&rcu_sched_state); + rcu_preempt_cleanup_dying_cpu(); rcu_cleanup_after_idle(cpu); break; case CPU_DEAD: case CPU_DEAD_FROZEN: case CPU_UP_CANCELED: case CPU_UP_CANCELED_FROZEN: - rcu_offline_cpu(cpu); + rcu_cleanup_dead_cpu(cpu, &rcu_bh_state); + rcu_cleanup_dead_cpu(cpu, &rcu_sched_state); + rcu_preempt_cleanup_dead_cpu(cpu); break; default: break; diff --git a/kernel/rcutree.h b/kernel/rcutree.h index af2af3cc5e65..05e03675439a 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -439,8 +439,8 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp); static int rcu_preempt_offline_tasks(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp); -static void rcu_preempt_offline_cpu(int cpu); #endif /* #ifdef CONFIG_HOTPLUG_CPU */ +static void rcu_preempt_cleanup_dead_cpu(int cpu); static void rcu_preempt_check_callbacks(int cpu); static void rcu_preempt_process_callbacks(void); void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)); @@ -451,7 +451,7 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, static int rcu_preempt_pending(int cpu); static int rcu_preempt_needs_cpu(int cpu); static void __cpuinit rcu_preempt_init_percpu_data(int cpu); -static void rcu_preempt_send_cbs_to_online(void); +static void rcu_preempt_cleanup_dying_cpu(void); static void __init __rcu_init_preempt(void); static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags); static void rcu_preempt_boost_start_gp(struct rcu_node *rnp); diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 7adf232bb66b..eeb2cc6b8657 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -618,16 +618,16 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp, return retval; } +#endif /* #ifdef CONFIG_HOTPLUG_CPU */ + /* * Do CPU-offline processing for preemptible RCU. */ -static void rcu_preempt_offline_cpu(int cpu) +static void rcu_preempt_cleanup_dead_cpu(int cpu) { - __rcu_offline_cpu(cpu, &rcu_preempt_state); + rcu_cleanup_dead_cpu(cpu, &rcu_preempt_state); } -#endif /* #ifdef CONFIG_HOTPLUG_CPU */ - /* * Check for a quiescent state from the current CPU. When a task blocks, * the task is recorded in the corresponding CPU's rcu_node structure, @@ -912,11 +912,12 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu) } /* - * Move preemptible RCU's callbacks from dying CPU to other online CPU. + * Move preemptible RCU's callbacks from dying CPU to other online CPU + * and record a quiescent state. */ -static void rcu_preempt_send_cbs_to_online(void) +static void rcu_preempt_cleanup_dying_cpu(void) { - rcu_send_cbs_to_online(&rcu_preempt_state); + rcu_cleanup_dying_cpu(&rcu_preempt_state); } /* @@ -1052,16 +1053,16 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp, return 0; } +#endif /* #ifdef CONFIG_HOTPLUG_CPU */ + /* * Because preemptible RCU does not exist, it never needs CPU-offline * processing. */ -static void rcu_preempt_offline_cpu(int cpu) +static void rcu_preempt_cleanup_dead_cpu(int cpu) { } -#endif /* #ifdef CONFIG_HOTPLUG_CPU */ - /* * Because preemptible RCU does not exist, it never has any callbacks * to check. @@ -1153,9 +1154,9 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu) } /* - * Because there is no preemptible RCU, there are no callbacks to move. + * Because there is no preemptible RCU, there is no cleanup to do. */ -static void rcu_preempt_send_cbs_to_online(void) +static void rcu_preempt_cleanup_dying_cpu(void) { } -- cgit v1.2.3 From 091541bbdb9906349481a504e7d8e7fa89f6b6bb Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 10 Jan 2012 12:51:14 -0800 Subject: rcu: Make rcutorture flag online/offline failures Make rcutorture check for CPU-hotplug failures and complain if there were any. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutorture.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'kernel') diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c index a58ac285fc69..a52b3217c160 100644 --- a/kernel/rcutorture.c +++ b/kernel/rcutorture.c @@ -1602,6 +1602,10 @@ rcu_torture_cleanup(void) cur_ops->cleanup(); if (atomic_read(&n_rcu_torture_error)) rcu_torture_print_module_parms(cur_ops, "End of test: FAILURE"); + else if (n_online_successes != n_online_attempts || + n_offline_successes != n_offline_attempts) + rcu_torture_print_module_parms(cur_ops, + "End of test: RCU_HOTPLUG"); else rcu_torture_print_module_parms(cur_ops, "End of test: SUCCESS"); } -- cgit v1.2.3 From 778d250a29224795e6320b58928bafa6b6104a06 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 10 Jan 2012 14:13:24 -0800 Subject: rcu: Limit lazy-callback duration Currently, a given CPU is permitted to remain in dyntick-idle mode indefinitely if it has only lazy RCU callbacks queued. This is vulnerable to corner cases in NUMA systems, so limit the time to six seconds by default. (Currently controlled by a cpp macro.) Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree_plugin.h | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) (limited to 'kernel') diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index eeb2cc6b8657..f8e6dcc91860 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -2050,6 +2050,9 @@ static void rcu_prepare_for_idle(int cpu) * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your * system. And if you are -that- concerned about energy efficiency, * just power the system down and be done with it! + * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is + * permitted to sleep in dyntick-idle mode with only lazy RCU + * callbacks pending. Setting this too high can OOM your system. * * The values below work well in practice. If future workloads require * adjustment, they can be converted into kernel config parameters, though @@ -2058,11 +2061,13 @@ static void rcu_prepare_for_idle(int cpu) #define RCU_IDLE_FLUSHES 5 /* Number of dyntick-idle tries. */ #define RCU_IDLE_OPT_FLUSHES 3 /* Optional dyntick-idle tries. */ #define RCU_IDLE_GP_DELAY 6 /* Roughly one grace period. */ +#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */ static DEFINE_PER_CPU(int, rcu_dyntick_drain); static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff); static DEFINE_PER_CPU(struct hrtimer, rcu_idle_gp_timer); -static ktime_t rcu_idle_gp_wait; +static ktime_t rcu_idle_gp_wait; /* If some non-lazy callbacks. */ +static ktime_t rcu_idle_lazy_gp_wait; /* If only lazy callbacks. */ /* * Allow the CPU to enter dyntick-idle mode if either: (1) There are no @@ -2151,6 +2156,8 @@ static void rcu_prepare_for_idle_init(int cpu) unsigned int upj = jiffies_to_usecs(RCU_IDLE_GP_DELAY); rcu_idle_gp_wait = ns_to_ktime(upj * (u64)1000); + upj = jiffies_to_usecs(RCU_IDLE_LAZY_GP_DELAY); + rcu_idle_lazy_gp_wait = ns_to_ktime(upj * (u64)1000); firsttime = 0; } } @@ -2225,6 +2232,9 @@ static void rcu_prepare_for_idle(int cpu) if (rcu_cpu_has_nonlazy_callbacks(cpu)) hrtimer_start(&per_cpu(rcu_idle_gp_timer, cpu), rcu_idle_gp_wait, HRTIMER_MODE_REL); + else + hrtimer_start(&per_cpu(rcu_idle_gp_timer, cpu), + rcu_idle_lazy_gp_wait, HRTIMER_MODE_REL); return; /* Nothing more to do immediately. */ } else if (--per_cpu(rcu_dyntick_drain, cpu) <= 0) { /* We have hit the limit, so time to give up. */ -- cgit v1.2.3 From 8146c4e2e2c1972216afece5c50e072e86120e42 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 10 Jan 2012 14:23:29 -0800 Subject: rcu: Check for callback invocation from offline CPUs Because quiescent states are now reported from offline CPUs in CPU_DYING state, there is some possibility that such a CPU might note the end of a grace period and attempt to start invoking callbacks. This would be a very bad thing, and is supposed to be prevented by the fact that the CPU_DYING CPU gets rid of all its callbacks before reporting the quiescent state. However, there is other CPU-offline code in the kernel, and it is quite possible that someone will invoke RCU core processing from that code. Therefore, this commit adds a warning for this case. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 1 + 1 file changed, 1 insertion(+) (limited to 'kernel') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 575f91d03f06..ac3a810d2db7 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1373,6 +1373,7 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp) * races with call_rcu() from interrupt handlers. */ local_irq_save(flags); + WARN_ON_ONCE(cpu_is_offline(smp_processor_id())); bl = rdp->blimit; trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl); list = rdp->nxtlist; -- cgit v1.2.3 From a50c3af910e06f35bc0c68f89d8fef98c0fec0ea Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 10 Jan 2012 17:52:31 -0800 Subject: rcu: Don't make callbacks go through second full grace period RCU's current CPU-offline code path dumps all of the outgoing CPU's callbacks onto the RCU_NEXT_TAIL portion of the surviving CPU's callback list. This means that all the ready-to-invoke callbacks from the outgoing CPU must wait for another full RCU grace period. This was just fine when CPU-hotplug events were rare, but there is increasing evidence that users are planning to make increasing use of CPU hotplug. Therefore, this commit changes the callback-dumping procedure so that callbacks that are ready to invoke are moved to the RCU_DONE_TAIL portion of the surviving CPU's callback list. This avoids running these callbacks through a second unnecessary grace period. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 46 insertions(+), 6 deletions(-) (limited to 'kernel') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index ac3a810d2db7..7789e666394d 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1270,24 +1270,64 @@ static void rcu_cleanup_dying_cpu(struct rcu_state *rsp) struct rcu_data *receive_rdp = per_cpu_ptr(rsp->rda, receive_cpu); struct rcu_node *rnp = rdp->mynode; /* For dying CPU. */ - /* Move callbacks to some other CPU. */ + /* First, adjust the counts. */ + if (rdp->nxtlist != NULL) { + receive_rdp->qlen_lazy += rdp->qlen_lazy; + receive_rdp->qlen += rdp->qlen; + rdp->qlen_lazy = 0; + rdp->qlen = 0; + } + + /* + * Next, move ready-to-invoke callbacks to be invoked on some + * other CPU. These will not be required to pass through another + * grace period: They are done, regardless of CPU. + */ + if (rdp->nxtlist != NULL && + rdp->nxttail[RCU_DONE_TAIL] != &rdp->nxtlist) { + struct rcu_head *oldhead; + struct rcu_head **oldtail; + struct rcu_head **newtail; + + oldhead = rdp->nxtlist; + oldtail = receive_rdp->nxttail[RCU_DONE_TAIL]; + rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL]; + *rdp->nxttail[RCU_DONE_TAIL] = *oldtail; + *receive_rdp->nxttail[RCU_DONE_TAIL] = oldhead; + newtail = rdp->nxttail[RCU_DONE_TAIL]; + for (i = RCU_DONE_TAIL; i < RCU_NEXT_SIZE; i++) { + if (receive_rdp->nxttail[i] == oldtail) + receive_rdp->nxttail[i] = newtail; + if (rdp->nxttail[i] == newtail) + rdp->nxttail[i] = &rdp->nxtlist; + } + } + + /* + * Finally, put the rest of the callbacks at the end of the list. + * The ones that made it partway through get to start over: We + * cannot assume that grace periods are synchronized across CPUs. + * (We could splice RCU_WAIT_TAIL into RCU_NEXT_READY_TAIL, but + * this does not seem compelling. Not yet, anyway.) + */ if (rdp->nxtlist != NULL) { *receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist; receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL]; - receive_rdp->qlen_lazy += rdp->qlen_lazy; - receive_rdp->qlen += rdp->qlen; receive_rdp->n_cbs_adopted += rdp->qlen; rdp->n_cbs_orphaned += rdp->qlen; rdp->nxtlist = NULL; for (i = 0; i < RCU_NEXT_SIZE; i++) rdp->nxttail[i] = &rdp->nxtlist; - rdp->qlen_lazy = 0; - rdp->qlen = 0; } - /* Record a quiescent state for the dying CPU. */ + /* + * Record a quiescent state for the dying CPU. This is safe + * only because we have already cleared out the callbacks. + * (Otherwise, the RCU core might try to schedule the invocation + * of callbacks on this now-offline CPU, which would be bad.) + */ mask = rdp->grpmask; /* rnp->grplo is constant. */ trace_rcu_grace_period(rsp->name, rnp->gpnum + 1 - !!(rnp->qsmask & mask), -- cgit v1.2.3 From f38bd1020f797694b6b5e06f5f06c87688fc84c0 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 11 Jan 2012 11:34:50 -0800 Subject: rcu: Remove single-rcu_node optimization in rcu_start_gp() The grace-period initialization sequence in rcu_start_gp() has a special case for systems where the rcu_node tree is a single rcu_node structure. This made sense some years ago when systems were smaller and up to 64 CPUs could share a single rcu_node structure, but now that large systems are common and a given leaf rcu_node structure can support only 16 CPUs (due to lock contention on the rcu_node's ->lock field), this optimization is almost never taken. And even the small mobile platforms that might make use of it might rather have the kernel text reduction. Therefore, this commit removes the check for single-rcu_node trees. Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree.c | 18 ------------------ 1 file changed, 18 deletions(-) (limited to 'kernel') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 7789e666394d..49bb363a0837 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -984,26 +984,8 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) rsp->fqs_state = RCU_GP_INIT; /* Hold off force_quiescent_state. */ rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS; record_gp_stall_check_time(rsp); - - /* Special-case the common single-level case. */ - if (NUM_RCU_NODES == 1) { - rcu_preempt_check_blocked_tasks(rnp); - rnp->qsmask = rnp->qsmaskinit; - rnp->gpnum = rsp->gpnum; - rnp->completed = rsp->completed; - rsp->fqs_state = RCU_SIGNAL_INIT; /* force_quiescent_state OK */ - rcu_start_gp_per_cpu(rsp, rnp, rdp); - rcu_preempt_boost_start_gp(rnp); - trace_rcu_grace_period_init(rsp->name, rnp->gpnum, - rnp->level, rnp->grplo, - rnp->grphi, rnp->qsmask); - raw_spin_unlock_irqrestore(&rnp->lock, flags); - return; - } - raw_spin_unlock(&rnp->lock); /* leave irqs disabled. */ - /* Exclude any concurrent CPU-hotplug operations. */ raw_spin_lock(&rsp->onofflock); /* irqs already disabled. */ -- cgit v1.2.3 From 26861faf896a4cfdc4243281e5c305755f4bad52 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 11 Jan 2012 14:40:20 -0800 Subject: rcu: Protect __rcu_read_unlock() against scheduler-using irq handlers This commit ports commit #10f39bb1b2 (rcu: protect __rcu_read_unlock() against scheduler-using irq handlers) from TREE_PREEMPT_RCU to TINY_PREEMPT_RCU. The following is a corresponding port of that commit message. The addition of RCU read-side critical sections within runqueue and priority-inheritance critical sections introduced some deadlocks, for example, involving interrupts from __rcu_read_unlock() where the interrupt handlers call wake_up(). This situation can cause the instance of __rcu_read_unlock() invoked from interrupt to do some of the processing that would otherwise have been carried out by the task-level instance of __rcu_read_unlock(). When the interrupt-level instance of __rcu_read_unlock() is called with a scheduler lock held from interrupt-entry/exit situations where in_irq() returns false, deadlock can result. Of course, in a UP kernel, there are not really any deadlocks, but the upper-level critical section can still be be fatally confused by the lower-level critical section changing things out from under it. This commit resolves these deadlocks by using negative values of the per-task ->rcu_read_lock_nesting counter to indicate that an instance of __rcu_read_unlock() is in flight, which in turn prevents instances from interrupt handlers from doing any special processing. Note that nested rcu_read_lock()/rcu_read_unlock() pairs are still permitted, but they will never see ->rcu_read_lock_nesting go to zero, and will therefore never invoke rcu_read_unlock_special(), thus preventing them from seeing the RCU_READ_UNLOCK_BLOCKED bit should it be set in ->rcu_read_unlock_special. This patch also adds a check for ->rcu_read_unlock_special being negative in rcu_check_callbacks(), thus preventing the RCU_READ_UNLOCK_NEED_QS bit from being set should a scheduling-clock interrupt occur while __rcu_read_unlock() is exiting from an outermost RCU read-side critical section. Of course, __rcu_read_unlock() can be preempted during the time that ->rcu_read_lock_nesting is negative. This could result in the setting of the RCU_READ_UNLOCK_BLOCKED bit after __rcu_read_unlock() checks it, and would also result it this task being queued on the corresponding rcu_node structure's blkd_tasks list. Therefore, some later RCU read-side critical section would enter rcu_read_unlock_special() to clean up -- which could result in deadlock (OK, OK, fatal confusion) if that RCU read-side critical section happened to be in the scheduler where the runqueue or priority-inheritance locks were held. To prevent the possibility of fatal confusion that might result from preemption during the time that ->rcu_read_lock_nesting is negative, this commit also makes rcu_preempt_note_context_switch() check for negative ->rcu_read_lock_nesting, thus refraining from queuing the task (and from setting RCU_READ_UNLOCK_BLOCKED) if we are already exiting from the outermost RCU read-side critical section (in other words, we really are no longer actually in that RCU read-side critical section). In addition, rcu_preempt_note_context_switch() invokes rcu_read_unlock_special() to carry out the cleanup in this case, which clears out the ->rcu_read_unlock_special bits and dequeues the task (if necessary), in turn avoiding needless delay of the current RCU grace period and needless RCU priority boosting. It is still illegal to call rcu_read_unlock() while holding a scheduler lock if the prior RCU read-side critical section has ever had both preemption and irqs enabled. However, the common use case is legal, namely where then entire RCU read-side critical section executes with irqs disabled, for example, when the scheduler lock is held across the entire lifetime of the RCU read-side critical section. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutiny_plugin.h | 43 +++++++++++++++++++++++++++++++++++-------- 1 file changed, 35 insertions(+), 8 deletions(-) (limited to 'kernel') diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h index 4b905404a5bd..432ed2bc05ad 100644 --- a/kernel/rcutiny_plugin.h +++ b/kernel/rcutiny_plugin.h @@ -132,6 +132,7 @@ static struct rcu_preempt_ctrlblk rcu_preempt_ctrlblk = { RCU_TRACE(.rcb.name = "rcu_preempt") }; +static void rcu_read_unlock_special(struct task_struct *t); static int rcu_preempted_readers_exp(void); static void rcu_report_exp_done(void); @@ -146,6 +147,16 @@ static int rcu_cpu_blocking_cur_gp(void) /* * Check for a running RCU reader. Because there is only one CPU, * there can be but one running RCU reader at a time. ;-) + * + * Returns zero if there are no running readers. Returns a positive + * number if there is at least one reader within its RCU read-side + * critical section. Returns a negative number if an outermost reader + * is in the midst of exiting from its RCU read-side critical section + * + * Returns zero if there are no running readers. Returns a positive + * number if there is at least one reader within its RCU read-side + * critical section. Returns a negative number if an outermost reader + * is in the midst of exiting from its RCU read-side critical section. */ static int rcu_preempt_running_reader(void) { @@ -475,7 +486,7 @@ void rcu_preempt_note_context_switch(void) unsigned long flags; local_irq_save(flags); /* must exclude scheduler_tick(). */ - if (rcu_preempt_running_reader() && + if (rcu_preempt_running_reader() > 0 && (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { /* Possibly blocking in an RCU read-side critical section. */ @@ -494,6 +505,13 @@ void rcu_preempt_note_context_switch(void) list_add(&t->rcu_node_entry, &rcu_preempt_ctrlblk.blkd_tasks); if (rcu_cpu_blocking_cur_gp()) rcu_preempt_ctrlblk.gp_tasks = &t->rcu_node_entry; + } else if (rcu_preempt_running_reader() < 0 && + t->rcu_read_unlock_special) { + /* + * Complete exit from RCU read-side critical section on + * behalf of preempted instance of __rcu_read_unlock(). + */ + rcu_read_unlock_special(t); } /* @@ -618,13 +636,22 @@ void __rcu_read_unlock(void) struct task_struct *t = current; barrier(); /* needed if we ever invoke rcu_read_unlock in rcutiny.c */ - --t->rcu_read_lock_nesting; - barrier(); /* decrement before load of ->rcu_read_unlock_special */ - if (t->rcu_read_lock_nesting == 0 && - unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) - rcu_read_unlock_special(t); + if (t->rcu_read_lock_nesting != 1) + --t->rcu_read_lock_nesting; + else { + t->rcu_read_lock_nesting = INT_MIN; + barrier(); /* assign before ->rcu_read_unlock_special load */ + if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) + rcu_read_unlock_special(t); + barrier(); /* ->rcu_read_unlock_special load before assign */ + t->rcu_read_lock_nesting = 0; + } #ifdef CONFIG_PROVE_LOCKING - WARN_ON_ONCE(t->rcu_read_lock_nesting < 0); + { + int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting); + + WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2); + } #endif /* #ifdef CONFIG_PROVE_LOCKING */ } EXPORT_SYMBOL_GPL(__rcu_read_unlock); @@ -649,7 +676,7 @@ static void rcu_preempt_check_callbacks(void) invoke_rcu_callbacks(); if (rcu_preempt_gp_in_progress() && rcu_cpu_blocking_cur_gp() && - rcu_preempt_running_reader()) + rcu_preempt_running_reader() > 0) t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS; } -- cgit v1.2.3 From afef20540f7cd1ea91bc1ac20be238389eee4003 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 11 Jan 2012 15:30:36 -0800 Subject: rcu: Streamline code produced by __rcu_read_unlock() This is a port of commit #be0e1e21 to TINY_PREEMPT_RCU. This uses noinline to prevent rcu_read_unlock_special() from being inlined into __rcu_read_unlock(). Signed-off-by: Paul E. McKenney --- kernel/rcutiny_plugin.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel') diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h index 432ed2bc05ad..b58a3200f0ff 100644 --- a/kernel/rcutiny_plugin.h +++ b/kernel/rcutiny_plugin.h @@ -544,7 +544,7 @@ EXPORT_SYMBOL_GPL(__rcu_read_lock); * notify RCU core processing or task having blocked during the RCU * read-side critical section. */ -static void rcu_read_unlock_special(struct task_struct *t) +static noinline void rcu_read_unlock_special(struct task_struct *t) { int empty; int empty_exp; -- cgit v1.2.3 From 768dfffdffbfcc07d6927bdd642c714c0dd64c99 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 11 Jan 2012 16:33:17 -0800 Subject: rcu: Prevent RCU callbacks from executing before scheduler initialized This is a port of commit #b0d3041 from TREE_RCU to TREE_PREEMPT_RCU. Under some rare but real combinations of configuration parameters, RCU callbacks are posted during early boot that use kernel facilities that are not yet initialized. Therefore, when these callbacks are invoked, hard hangs and crashes ensue. This commit therefore prevents RCU callbacks from being invoked until after the scheduler is fully up and running, as in after multiple tasks have been spawned. It might well turn out that a better approach is to identify the specific RCU callbacks that are causing this problem, but that discussion will wait until such time as someone really needs an RCU callback to be invoked (as opposed to merely registered) during early boot. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- include/linux/rcutiny.h | 4 ---- kernel/rcutiny_plugin.h | 15 ++++++++++++--- 2 files changed, 12 insertions(+), 7 deletions(-) (limited to 'kernel') diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index 51bf29c81485..e93df77176d1 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -27,13 +27,9 @@ #include -#ifdef CONFIG_RCU_BOOST static inline void rcu_init(void) { } -#else /* #ifdef CONFIG_RCU_BOOST */ -void rcu_init(void); -#endif /* #else #ifdef CONFIG_RCU_BOOST */ static inline void rcu_barrier_bh(void) { diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h index b58a3200f0ff..95df60ebe363 100644 --- a/kernel/rcutiny_plugin.h +++ b/kernel/rcutiny_plugin.h @@ -914,7 +914,8 @@ static void rcu_preempt_process_callbacks(void) static void invoke_rcu_callbacks(void) { have_rcu_kthread_work = 1; - wake_up(&rcu_kthread_wq); + if (rcu_kthread_task != NULL) + wake_up(&rcu_kthread_wq); } #ifdef CONFIG_RCU_TRACE @@ -975,12 +976,16 @@ early_initcall(rcu_spawn_kthreads); #else /* #ifdef CONFIG_RCU_BOOST */ +/* Hold off callback invocation until early_initcall() time. */ +static int rcu_scheduler_fully_active __read_mostly; + /* * Start up softirq processing of callbacks. */ void invoke_rcu_callbacks(void) { - raise_softirq(RCU_SOFTIRQ); + if (rcu_scheduler_fully_active) + raise_softirq(RCU_SOFTIRQ); } #ifdef CONFIG_RCU_TRACE @@ -995,10 +1000,14 @@ static bool rcu_is_callbacks_kthread(void) #endif /* #ifdef CONFIG_RCU_TRACE */ -void rcu_init(void) +static int __init rcu_scheduler_really_started(void) { + rcu_scheduler_fully_active = 1; open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); + raise_softirq(RCU_SOFTIRQ); /* Invoke any callbacks from early boot. */ + return 0; } +early_initcall(rcu_scheduler_really_started); #endif /* #else #ifdef CONFIG_RCU_BOOST */ -- cgit v1.2.3 From 8762705ad4ac860bb78434409df463d02ac8f027 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 11 Jan 2012 16:59:01 -0800 Subject: rcu: Inform RCU of irq_exit() activity This is a port to TINY_RCU of Peter Zijlstra's commit #ec433f0c5 The rcu_read_unlock_special() function relies on in_irq() to exclude scheduler activity from interrupt level. This fails because exit_irq() can invoke the scheduler after clearing the preempt_count() bits that in_irq() uses to determine that it is at interrupt level. This situation can result in failures as follows: $task IRQ SoftIRQ rcu_read_lock() /* do stuff */ |= UNLOCK_BLOCKED rcu_read_unlock() --t->rcu_read_lock_nesting irq_enter(); /* do stuff, don't use RCU */ irq_exit(); sub_preempt_count(IRQ_EXIT_OFFSET); invoke_softirq() ttwu(); spin_lock_irq(&pi->lock) rcu_read_lock(); /* do stuff */ rcu_read_unlock(); rcu_read_unlock_special() rcu_report_exp_rnp() ttwu() spin_lock_irq(&pi->lock) /* deadlock */ rcu_read_unlock_special(t); This can be triggered 'easily' because invoke_softirq() immediately does a ttwu() of ksoftirqd/# instead of doing the in-place softirq stuff first, but even without that the above happens. Cure this by also excluding softirqs from the rcu_read_unlock_special() handler and ensuring the force_irqthreads ksoftirqd/# wakeup is done from full softirq context. It is also necessary to delay the ->rcu_read_lock_nesting decrement until after rcu_read_unlock_special(). This delay is handled by the commit "Protect __rcu_read_unlock() against scheduler-using irq handlers". Signed-off-by: Peter Zijlstra Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutiny_plugin.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel') diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h index 95df60ebe363..387c2759e1b0 100644 --- a/kernel/rcutiny_plugin.h +++ b/kernel/rcutiny_plugin.h @@ -570,7 +570,7 @@ static noinline void rcu_read_unlock_special(struct task_struct *t) rcu_preempt_cpu_qs(); /* Hardware IRQ handlers cannot block. */ - if (in_irq()) { + if (in_irq() || in_serving_softirq()) { local_irq_restore(flags); return; } -- cgit v1.2.3 From 1aa03f1188f7b0b85df2de602b33ee7b6fab8e00 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 11 Jan 2012 17:25:17 -0800 Subject: rcu: Simplify unboosting checks This is a port of commit #82e78d80 from TREE_PREEMPT_RCU to TINY_PREEMPT_RCU. This commit uses the fact that current->rcu_boost_mutex is set any time that the RCU_READ_UNLOCK_BOOSTED flag is set in the current->rcu_read_unlock_special bitmask. This allows tests of the bit to be changed to tests of the pointer, which in turn allows the RCU_READ_UNLOCK_BOOSTED flag to be eliminated. Please note that the check of current->rcu_read_unlock_special need not change because any time that RCU_READ_UNLOCK_BOOSTED was set, so was RCU_READ_UNLOCK_BLOCKED. Therefore, __rcu_read_unlock() can continue testing current->rcu_read_unlock_special for non-zero, as before. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- include/linux/sched.h | 3 +-- kernel/rcutiny_plugin.h | 10 ++++++---- 2 files changed, 7 insertions(+), 6 deletions(-) (limited to 'kernel') diff --git a/include/linux/sched.h b/include/linux/sched.h index 7d379a6bfd88..e692abaf915a 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1864,8 +1864,7 @@ extern void task_clear_jobctl_pending(struct task_struct *task, #ifdef CONFIG_PREEMPT_RCU #define RCU_READ_UNLOCK_BLOCKED (1 << 0) /* blocked while in RCU read-side. */ -#define RCU_READ_UNLOCK_BOOSTED (1 << 1) /* boosted while in RCU read-side. */ -#define RCU_READ_UNLOCK_NEED_QS (1 << 2) /* RCU core needs CPU response. */ +#define RCU_READ_UNLOCK_NEED_QS (1 << 1) /* RCU core needs CPU response. */ static inline void rcu_copy_process(struct task_struct *p) { diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h index 387c2759e1b0..22ecea0dfb62 100644 --- a/kernel/rcutiny_plugin.h +++ b/kernel/rcutiny_plugin.h @@ -318,7 +318,6 @@ static int rcu_boost(void) t = container_of(tb, struct task_struct, rcu_node_entry); rt_mutex_init_proxy_locked(&mtx, t); t->rcu_boost_mutex = &mtx; - t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BOOSTED; raw_local_irq_restore(flags); rt_mutex_lock(&mtx); rt_mutex_unlock(&mtx); /* Keep lockdep happy. */ @@ -550,6 +549,9 @@ static noinline void rcu_read_unlock_special(struct task_struct *t) int empty_exp; unsigned long flags; struct list_head *np; +#ifdef CONFIG_RCU_BOOST + struct rt_mutex *rbmp = NULL; +#endif /* #ifdef CONFIG_RCU_BOOST */ int special; /* @@ -615,10 +617,10 @@ static noinline void rcu_read_unlock_special(struct task_struct *t) } #ifdef CONFIG_RCU_BOOST /* Unboost self if was boosted. */ - if (special & RCU_READ_UNLOCK_BOOSTED) { - t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BOOSTED; - rt_mutex_unlock(t->rcu_boost_mutex); + if (t->rcu_boost_mutex != NULL) { + rbmp = t->rcu_boost_mutex; t->rcu_boost_mutex = NULL; + rt_mutex_unlock(rbmp); } #endif /* #ifdef CONFIG_RCU_BOOST */ local_irq_restore(flags); -- cgit v1.2.3 From 30fbcc90b02187c55c57ff0ecf57cecbd487d694 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 12 Jan 2012 11:01:14 -0800 Subject: rcu: Clean up straggling rcu_preempt_needs_cpu() name The recent updates to RCU_CPU_FAST_NO_HZ have an rcu_needs_cpu() that does more than just check for callbacks, so get the name for rcu_preempt_needs_cpu() consistent with that change, now calling it rcu_preempt_cpu_has_callbacks(). Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 2 +- kernel/rcutree.h | 2 +- kernel/rcutree_plugin.h | 8 ++++---- 3 files changed, 6 insertions(+), 6 deletions(-) (limited to 'kernel') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 49bb363a0837..0569ba11e35a 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1958,7 +1958,7 @@ static int rcu_cpu_has_callbacks(int cpu) /* RCU callbacks either ready or pending? */ return per_cpu(rcu_sched_data, cpu).nxtlist || per_cpu(rcu_bh_data, cpu).nxtlist || - rcu_preempt_needs_cpu(cpu); + rcu_preempt_cpu_has_callbacks(cpu); } static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL}; diff --git a/kernel/rcutree.h b/kernel/rcutree.h index 05e03675439a..58c9fc3bc820 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -449,7 +449,7 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, bool wake); #endif /* #if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_TREE_PREEMPT_RCU) */ static int rcu_preempt_pending(int cpu); -static int rcu_preempt_needs_cpu(int cpu); +static int rcu_preempt_cpu_has_callbacks(int cpu); static void __cpuinit rcu_preempt_init_percpu_data(int cpu); static void rcu_preempt_cleanup_dying_cpu(void); static void __init __rcu_init_preempt(void); diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index f8e6dcc91860..297d561c3e4b 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -887,9 +887,9 @@ static int rcu_preempt_pending(int cpu) } /* - * Does preemptible RCU need the CPU to stay out of dynticks mode? + * Does preemptible RCU have callbacks on this CPU? */ -static int rcu_preempt_needs_cpu(int cpu) +static int rcu_preempt_cpu_has_callbacks(int cpu) { return !!per_cpu(rcu_preempt_data, cpu).nxtlist; } @@ -1128,9 +1128,9 @@ static int rcu_preempt_pending(int cpu) } /* - * Because preemptible RCU does not exist, it never needs any CPU. + * Because preemptible RCU does not exist, it never has callbacks */ -static int rcu_preempt_needs_cpu(int cpu) +static int rcu_preempt_cpu_has_callbacks(int cpu) { return 0; } -- cgit v1.2.3 From c44e2cddacc2cf299186bad5697d738ea19668b7 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 12 Jan 2012 13:08:18 -0800 Subject: rcu: Check for idle-loop entry while in RCU read-side critical section The inner idle loop is an extended quiescent state for all flavors of RCU, but there have been recent bug involving use of RCU read-side primitives from within the idle loop. Therefore, this commit enlists lockdep-RCU to detect attempts to enter the inner idle loop while in an RCU read-side critical section, emitting a lockdep-RCU splat if so. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 11 +++++++++++ 1 file changed, 11 insertions(+) (limited to 'kernel') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 0569ba11e35a..195bf1fb59ea 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -366,6 +366,17 @@ static void rcu_idle_enter_common(struct rcu_dynticks *rdtp, long long oldval) atomic_inc(&rdtp->dynticks); smp_mb__after_atomic_inc(); /* Force ordering with next sojourn. */ WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1); + + /* + * The idle task is not permitted to enter the idle loop while + * in an RCU read-side critical section. + */ + rcu_lockdep_assert(!lock_is_held(&rcu_lock_map), + "Illegal idle entry in RCU read-side critical section."); + rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map), + "Illegal idle entry in RCU-bh read-side critical section."); + rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map), + "Illegal idle entry in RCU-sched read-side critical section."); } /** -- cgit v1.2.3 From 27565d64a4e564e72c22d8c91a3cfcb9442383e8 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 12 Jan 2012 19:35:08 -0800 Subject: rcu: Remove #ifdef CONFIG_SMP from TREE_RCU Now that both TINY_RCU and TINY_PREEMPT_RCU have been in place for awhile, it is time to remove UP support from TREE_RCU, which is what this commit does. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 19 ------------------- kernel/rcutree_plugin.h | 12 ------------ 2 files changed, 31 deletions(-) (limited to 'kernel') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 195bf1fb59ea..61adb351d2c7 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -301,8 +301,6 @@ static struct rcu_node *rcu_get_root(struct rcu_state *rsp) return &rsp->node[0]; } -#ifdef CONFIG_SMP - /* * If the specified CPU is offline, tell the caller that it is in * a quiescent state. Otherwise, whack it with a reschedule IPI. @@ -339,8 +337,6 @@ static int rcu_implicit_offline_qs(struct rcu_data *rdp) return 0; } -#endif /* #ifdef CONFIG_SMP */ - /* * rcu_idle_enter_common - inform RCU that current CPU is moving towards idle * @@ -606,8 +602,6 @@ int rcu_is_cpu_rrupt_from_idle(void) return __get_cpu_var(rcu_dynticks).dynticks_nesting <= 1; } -#ifdef CONFIG_SMP - /* * Snapshot the specified CPU's dynticks counter so that we can later * credit them with an implicit quiescent state. Return 1 if this CPU @@ -651,8 +645,6 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) return rcu_implicit_offline_qs(rdp); } -#endif /* #ifdef CONFIG_SMP */ - static void record_gp_stall_check_time(struct rcu_state *rsp) { rsp->gp_start = jiffies; @@ -1517,8 +1509,6 @@ void rcu_check_callbacks(int cpu, int user) trace_rcu_utilization("End scheduler-tick"); } -#ifdef CONFIG_SMP - /* * Scan the leaf rcu_node structures, processing dyntick state for any that * have not yet encountered a quiescent state, using the function specified. @@ -1641,15 +1631,6 @@ unlock_fqs_ret: trace_rcu_utilization("End fqs"); } -#else /* #ifdef CONFIG_SMP */ - -static void force_quiescent_state(struct rcu_state *rsp, int relaxed) -{ - set_need_resched(); -} - -#endif /* #else #ifdef CONFIG_SMP */ - /* * This does the RCU core processing work for the specified rcu_state * and rcu_data structures. This may be called only from the CPU to diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 297d561c3e4b..0e74e1c6333f 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -1858,16 +1858,6 @@ static void __cpuinit rcu_prepare_kthreads(int cpu) #endif /* #else #ifdef CONFIG_RCU_BOOST */ -#ifndef CONFIG_SMP - -void synchronize_sched_expedited(void) -{ - cond_resched(); -} -EXPORT_SYMBOL_GPL(synchronize_sched_expedited); - -#else /* #ifndef CONFIG_SMP */ - static atomic_t sync_sched_expedited_started = ATOMIC_INIT(0); static atomic_t sync_sched_expedited_done = ATOMIC_INIT(0); @@ -1982,8 +1972,6 @@ void synchronize_sched_expedited(void) } EXPORT_SYMBOL_GPL(synchronize_sched_expedited); -#endif /* #else #ifndef CONFIG_SMP */ - #if !defined(CONFIG_RCU_FAST_NO_HZ) /* -- cgit v1.2.3 From 13cfcca0e4e2d4cee1d0183c049eb34e54ac976e Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 13 Jan 2012 15:32:18 -0800 Subject: rcu: Set RCU CPU stall times via sysfs The default CONFIG_RCU_CPU_STALL_TIMEOUT value of 60 seconds has served Linux users well for production use for quite some time. However, for debugging, there will be more than three minutes between subsequent stall-warning messages. This can be an annoyingly long wait if you are trying to work out where the offending infinite loop is hiding. Therefore, this commit provides a rcu_cpu_stall_timeout sysfs parameter that may be adjusted at boot time and at runtime to speed up debugging. Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 31 ++++++++++++++++++++++++++----- kernel/rcutree.h | 6 ------ 2 files changed, 26 insertions(+), 11 deletions(-) (limited to 'kernel') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 61adb351d2c7..cfdab9898e33 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -208,8 +208,11 @@ module_param(blimit, int, 0); module_param(qhimark, int, 0); module_param(qlowmark, int, 0); -int rcu_cpu_stall_suppress __read_mostly; +int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */ +int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT; + module_param(rcu_cpu_stall_suppress, int, 0644); +module_param(rcu_cpu_stall_timeout, int, 0644); static void force_quiescent_state(struct rcu_state *rsp, int relaxed); static int rcu_pending(int cpu); @@ -645,10 +648,28 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) return rcu_implicit_offline_qs(rdp); } +static int jiffies_till_stall_check(void) +{ + int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout); + + /* + * Limit check must be consistent with the Kconfig limits + * for CONFIG_RCU_CPU_STALL_TIMEOUT. + */ + if (till_stall_check < 3) { + ACCESS_ONCE(rcu_cpu_stall_timeout) = 3; + till_stall_check = 3; + } else if (till_stall_check > 300) { + ACCESS_ONCE(rcu_cpu_stall_timeout) = 300; + till_stall_check = 300; + } + return till_stall_check * HZ + RCU_STALL_DELAY_DELTA; +} + static void record_gp_stall_check_time(struct rcu_state *rsp) { rsp->gp_start = jiffies; - rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_CHECK; + rsp->jiffies_stall = jiffies + jiffies_till_stall_check(); } static void print_other_cpu_stall(struct rcu_state *rsp) @@ -667,7 +688,7 @@ static void print_other_cpu_stall(struct rcu_state *rsp) raw_spin_unlock_irqrestore(&rnp->lock, flags); return; } - rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_RECHECK; + rsp->jiffies_stall = jiffies + 3 * jiffies_till_stall_check() + 3; /* * Now rat on any tasks that got kicked up to the root rcu_node @@ -726,8 +747,8 @@ static void print_cpu_stall(struct rcu_state *rsp) raw_spin_lock_irqsave(&rnp->lock, flags); if (ULONG_CMP_GE(jiffies, rsp->jiffies_stall)) - rsp->jiffies_stall = - jiffies + RCU_SECONDS_TILL_STALL_RECHECK; + rsp->jiffies_stall = jiffies + + 3 * jiffies_till_stall_check() + 3; raw_spin_unlock_irqrestore(&rnp->lock, flags); set_need_resched(); /* kick ourselves to get things going. */ diff --git a/kernel/rcutree.h b/kernel/rcutree.h index 58c9fc3bc820..0328a537846a 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -314,12 +314,6 @@ struct rcu_data { #else #define RCU_STALL_DELAY_DELTA 0 #endif - -#define RCU_SECONDS_TILL_STALL_CHECK (CONFIG_RCU_CPU_STALL_TIMEOUT * HZ + \ - RCU_STALL_DELAY_DELTA) - /* for rsp->jiffies_stall */ -#define RCU_SECONDS_TILL_STALL_RECHECK (3 * RCU_SECONDS_TILL_STALL_CHECK + 30) - /* for rsp->jiffies_stall */ #define RCU_STALL_RAT_DELAY 2 /* Allow other CPUs time */ /* to take at least one */ /* scheduling clock irq */ -- cgit v1.2.3 From a858af2875fb291d0f4b0a4419fefbf03c2379c0 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 16 Jan 2012 13:29:10 -0800 Subject: rcu: Print scheduling-clock information on RCU CPU stall-warning messages There have been situations where RCU CPU stall warnings were caused by issues in scheduling-clock timer initialization. To make it easier to track these down, this commit causes the RCU CPU stall-warning messages to print out the number of scheduling-clock interrupts taken in the current grace period for each stalled CPU. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 33 +++++++---- kernel/rcutree.h | 11 ++++ kernel/rcutree_plugin.h | 150 +++++++++++++++++++++++++++++++++++++++++++++++- lib/Kconfig.debug | 14 +++++ 4 files changed, 194 insertions(+), 14 deletions(-) (limited to 'kernel') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index cfdab9898e33..dccd2f78db4e 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -689,12 +689,6 @@ static void print_other_cpu_stall(struct rcu_state *rsp) return; } rsp->jiffies_stall = jiffies + 3 * jiffies_till_stall_check() + 3; - - /* - * Now rat on any tasks that got kicked up to the root rcu_node - * due to CPU offlining. - */ - ndetected = rcu_print_task_stall(rnp); raw_spin_unlock_irqrestore(&rnp->lock, flags); /* @@ -702,8 +696,9 @@ static void print_other_cpu_stall(struct rcu_state *rsp) * See Documentation/RCU/stallwarn.txt for info on how to debug * RCU CPU stall warnings. */ - printk(KERN_ERR "INFO: %s detected stalls on CPUs/tasks: {", + printk(KERN_ERR "INFO: %s detected stalls on CPUs/tasks:", rsp->name); + print_cpu_stall_info_begin(); rcu_for_each_leaf_node(rsp, rnp) { raw_spin_lock_irqsave(&rnp->lock, flags); ndetected += rcu_print_task_stall(rnp); @@ -712,11 +707,22 @@ static void print_other_cpu_stall(struct rcu_state *rsp) continue; for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++) if (rnp->qsmask & (1UL << cpu)) { - printk(" %d", rnp->grplo + cpu); + print_cpu_stall_info(rsp, rnp->grplo + cpu); ndetected++; } } - printk("} (detected by %d, t=%ld jiffies)\n", + + /* + * Now rat on any tasks that got kicked up to the root rcu_node + * due to CPU offlining. + */ + rnp = rcu_get_root(rsp); + raw_spin_lock_irqsave(&rnp->lock, flags); + ndetected = rcu_print_task_stall(rnp); + raw_spin_unlock_irqrestore(&rnp->lock, flags); + + print_cpu_stall_info_end(); + printk(KERN_CONT "(detected by %d, t=%ld jiffies)\n", smp_processor_id(), (long)(jiffies - rsp->gp_start)); if (ndetected == 0) printk(KERN_ERR "INFO: Stall ended before state dump start\n"); @@ -740,8 +746,11 @@ static void print_cpu_stall(struct rcu_state *rsp) * See Documentation/RCU/stallwarn.txt for info on how to debug * RCU CPU stall warnings. */ - printk(KERN_ERR "INFO: %s detected stall on CPU %d (t=%lu jiffies)\n", - rsp->name, smp_processor_id(), jiffies - rsp->gp_start); + printk(KERN_ERR "INFO: %s self-detected stall on CPU", rsp->name); + print_cpu_stall_info_begin(); + print_cpu_stall_info(rsp, smp_processor_id()); + print_cpu_stall_info_end(); + printk(KERN_CONT " (t=%lu jiffies)\n", jiffies - rsp->gp_start); if (!trigger_all_cpu_backtrace()) dump_stack(); @@ -831,6 +840,7 @@ static void __note_new_gpnum(struct rcu_state *rsp, struct rcu_node *rnp, struct rdp->passed_quiesce = 0; } else rdp->qs_pending = 0; + zero_cpu_stall_ticks(rdp); } } @@ -1496,6 +1506,7 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp) void rcu_check_callbacks(int cpu, int user) { trace_rcu_utilization("Start scheduler-tick"); + increment_cpu_stall_ticks(); if (user || rcu_is_cpu_rrupt_from_idle()) { /* diff --git a/kernel/rcutree.h b/kernel/rcutree.h index 0328a537846a..e2ac8ee415bb 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -239,6 +239,12 @@ struct rcu_data { bool preemptible; /* Preemptible RCU? */ struct rcu_node *mynode; /* This CPU's leaf of hierarchy */ unsigned long grpmask; /* Mask to apply to leaf qsmask. */ +#ifdef CONFIG_RCU_CPU_STALL_INFO + unsigned long ticks_this_gp; /* The number of scheduling-clock */ + /* ticks this CPU has handled */ + /* during and after the last grace */ + /* period it is aware of. */ +#endif /* #ifdef CONFIG_RCU_CPU_STALL_INFO */ /* 2) batch handling */ /* @@ -466,5 +472,10 @@ static void __cpuinit rcu_prepare_kthreads(int cpu); static void rcu_prepare_for_idle_init(int cpu); static void rcu_cleanup_after_idle(int cpu); static void rcu_prepare_for_idle(int cpu); +static void print_cpu_stall_info_begin(void); +static void print_cpu_stall_info(struct rcu_state *rsp, int cpu); +static void print_cpu_stall_info_end(void); +static void zero_cpu_stall_ticks(struct rcu_data *rdp); +static void increment_cpu_stall_ticks(void); #endif /* #ifndef RCU_TREE_NONCORE */ diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 0e74e1c6333f..aa93b074bb2f 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -63,7 +63,10 @@ static void __init rcu_bootup_announce_oddness(void) printk(KERN_INFO "\tRCU torture testing starts during boot.\n"); #endif #if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE) - printk(KERN_INFO "\tVerbose stalled-CPUs detection is disabled.\n"); + printk(KERN_INFO "\tDump stacks of tasks blocking RCU-preempt GP.\n"); +#endif +#if defined(CONFIG_RCU_CPU_STALL_INFO) + printk(KERN_INFO "\tAdditional per-CPU info printed with stalls.\n"); #endif #if NUM_RCU_LVL_4 != 0 printk(KERN_INFO "\tExperimental four-level hierarchy is enabled.\n"); @@ -490,6 +493,31 @@ static void rcu_print_detail_task_stall(struct rcu_state *rsp) #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ +#ifdef CONFIG_RCU_CPU_STALL_INFO + +static void rcu_print_task_stall_begin(struct rcu_node *rnp) +{ + printk(KERN_ERR "\tTasks blocked on level-%d rcu_node (CPUs %d-%d):", + rnp->level, rnp->grplo, rnp->grphi); +} + +static void rcu_print_task_stall_end(void) +{ + printk(KERN_CONT "\n"); +} + +#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */ + +static void rcu_print_task_stall_begin(struct rcu_node *rnp) +{ +} + +static void rcu_print_task_stall_end(void) +{ +} + +#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */ + /* * Scan the current list of tasks blocked within RCU read-side critical * sections, printing out the tid of each. @@ -501,12 +529,14 @@ static int rcu_print_task_stall(struct rcu_node *rnp) if (!rcu_preempt_blocked_readers_cgp(rnp)) return 0; + rcu_print_task_stall_begin(rnp); t = list_entry(rnp->gp_tasks, struct task_struct, rcu_node_entry); list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { - printk(" P%d", t->pid); + printk(KERN_CONT " P%d", t->pid); ndetected++; } + rcu_print_task_stall_end(); return ndetected; } @@ -2004,7 +2034,7 @@ static void rcu_cleanup_after_idle(int cpu) } /* - * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=y, + * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n, * is nothing. */ static void rcu_prepare_for_idle(int cpu) @@ -2273,3 +2303,117 @@ static void rcu_prepare_for_idle(int cpu) } #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ + +#ifdef CONFIG_RCU_CPU_STALL_INFO + +#ifdef CONFIG_RCU_FAST_NO_HZ + +static void print_cpu_stall_fast_no_hz(char *cp, int cpu) +{ + struct hrtimer *hrtp = &per_cpu(rcu_idle_gp_timer, cpu); + + sprintf(cp, "drain=%d %c timer=%lld", + per_cpu(rcu_dyntick_drain, cpu), + per_cpu(rcu_dyntick_holdoff, cpu) == jiffies ? 'H' : '.', + hrtimer_active(hrtp) + ? ktime_to_us(hrtimer_get_remaining(hrtp)) + : -1); +} + +#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */ + +static void print_cpu_stall_fast_no_hz(char *cp, int cpu) +{ +} + +#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */ + +/* Initiate the stall-info list. */ +static void print_cpu_stall_info_begin(void) +{ + printk(KERN_CONT "\n"); +} + +/* + * Print out diagnostic information for the specified stalled CPU. + * + * If the specified CPU is aware of the current RCU grace period + * (flavor specified by rsp), then print the number of scheduling + * clock interrupts the CPU has taken during the time that it has + * been aware. Otherwise, print the number of RCU grace periods + * that this CPU is ignorant of, for example, "1" if the CPU was + * aware of the previous grace period. + * + * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info. + */ +static void print_cpu_stall_info(struct rcu_state *rsp, int cpu) +{ + char fast_no_hz[72]; + struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); + struct rcu_dynticks *rdtp = rdp->dynticks; + char *ticks_title; + unsigned long ticks_value; + + if (rsp->gpnum == rdp->gpnum) { + ticks_title = "ticks this GP"; + ticks_value = rdp->ticks_this_gp; + } else { + ticks_title = "GPs behind"; + ticks_value = rsp->gpnum - rdp->gpnum; + } + print_cpu_stall_fast_no_hz(fast_no_hz, cpu); + printk(KERN_ERR "\t%d: (%lu %s) idle=%03x/%llx/%d %s\n", + cpu, ticks_value, ticks_title, + atomic_read(&rdtp->dynticks) & 0xfff, + rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting, + fast_no_hz); +} + +/* Terminate the stall-info list. */ +static void print_cpu_stall_info_end(void) +{ + printk(KERN_ERR "\t"); +} + +/* Zero ->ticks_this_gp for all flavors of RCU. */ +static void zero_cpu_stall_ticks(struct rcu_data *rdp) +{ + rdp->ticks_this_gp = 0; +} + +/* Increment ->ticks_this_gp for all flavors of RCU. */ +static void increment_cpu_stall_ticks(void) +{ + __get_cpu_var(rcu_sched_data).ticks_this_gp++; + __get_cpu_var(rcu_bh_data).ticks_this_gp++; +#ifdef CONFIG_TREE_PREEMPT_RCU + __get_cpu_var(rcu_preempt_data).ticks_this_gp++; +#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */ +} + +#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */ + +static void print_cpu_stall_info_begin(void) +{ + printk(KERN_CONT " {"); +} + +static void print_cpu_stall_info(struct rcu_state *rsp, int cpu) +{ + printk(KERN_CONT " %d", cpu); +} + +static void print_cpu_stall_info_end(void) +{ + printk(KERN_CONT "} "); +} + +static void zero_cpu_stall_ticks(struct rcu_data *rdp) +{ +} + +static void increment_cpu_stall_ticks(void) +{ +} + +#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */ diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 3cc419d05f2f..d27a2aa3e815 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -927,6 +927,20 @@ config RCU_CPU_STALL_VERBOSE Say Y if you want to enable such checks. +config RCU_CPU_STALL_INFO + bool "Print additional diagnostics on RCU CPU stall" + depends on (TREE_RCU || TREE_PREEMPT_RCU) && DEBUG_KERNEL + default n + help + For each stalled CPU that is aware of the current RCU grace + period, print out additional per-CPU diagnostic information + regarding scheduling-clock ticks, idle state, and, + for RCU_FAST_NO_HZ kernels, idle-entry state. + + Say N if you are unsure. + + Say Y if you want to enable such diagnostics. + config RCU_TRACE bool "Enable tracing for RCU" depends on DEBUG_KERNEL -- cgit v1.2.3 From 9b9ec9b90ef481e182927989963274dc2697f9a6 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 17 Jan 2012 14:36:51 -0800 Subject: rcutorture: Permit holding off CPU-hotplug operations during boot When rcutorture is started automatically at boot time, it might well also start CPU-hotplug operations at that time, which might not be desirable. This commit therefore adds an rcutorture parameter that allows CPU-hotplug operations to be held off for the specified number of seconds after the start of boot. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- Documentation/RCU/torture.txt | 13 +++++++++++-- kernel/rcutorture.c | 12 ++++++++++-- 2 files changed, 21 insertions(+), 4 deletions(-) (limited to 'kernel') diff --git a/Documentation/RCU/torture.txt b/Documentation/RCU/torture.txt index d67068d0d2b9..01a809b1dbc6 100644 --- a/Documentation/RCU/torture.txt +++ b/Documentation/RCU/torture.txt @@ -69,6 +69,13 @@ onoff_interval CPU-hotplug operations regardless of what value is specified for onoff_interval. +onoff_holdoff The number of seconds to wait until starting CPU-hotplug + operations. This would normally only be used when + rcutorture was built into the kernel and started + automatically at boot time, in which case it is useful + in order to avoid confusing boot-time code with CPUs + coming and going. + shuffle_interval The number of seconds to keep the test threads affinitied to a particular subset of the CPUs, defaults to 3 seconds. @@ -277,5 +284,7 @@ The following script may be used to torture RCU: The output can be manually inspected for the error flag of "!!!". One could of course create a more elaborate script that automatically -checked for such errors. The "rmmod" command forces a "SUCCESS" or -"FAILURE" indication to be printk()ed. +checked for such errors. The "rmmod" command forces a "SUCCESS", +"FAILURE", or "RCU_HOTPLUG" indication to be printk()ed. The first +two are self-explanatory, while the last indicates that while there +were no RCU failures, CPU-hotplug problems were detected. diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c index a52b3217c160..2914cafe171b 100644 --- a/kernel/rcutorture.c +++ b/kernel/rcutorture.c @@ -65,6 +65,7 @@ static int fqs_duration; /* Duration of bursts (us), 0 to disable. */ static int fqs_holdoff; /* Hold time within burst (us). */ static int fqs_stutter = 3; /* Wait time between bursts (s). */ static int onoff_interval; /* Wait time between CPU hotplugs, 0=disable. */ +static int onoff_holdoff; /* Seconds after boot before CPU hotplugs. */ static int shutdown_secs; /* Shutdown time (s). <=0 for no shutdown. */ static int test_boost = 1; /* Test RCU prio boost: 0=no, 1=maybe, 2=yes. */ static int test_boost_interval = 7; /* Interval between boost tests, seconds. */ @@ -95,6 +96,8 @@ module_param(fqs_stutter, int, 0444); MODULE_PARM_DESC(fqs_stutter, "Wait time between fqs bursts (s)"); module_param(onoff_interval, int, 0444); MODULE_PARM_DESC(onoff_interval, "Time between CPU hotplugs (s), 0=disable"); +module_param(onoff_holdoff, int, 0444); +MODULE_PARM_DESC(onoff_holdoff, "Time after boot before CPU hotplugs (s)"); module_param(shutdown_secs, int, 0444); MODULE_PARM_DESC(shutdown_secs, "Shutdown time (s), zero to disable."); module_param(test_boost, int, 0444); @@ -1300,13 +1303,13 @@ rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, char *tag) "fqs_duration=%d fqs_holdoff=%d fqs_stutter=%d " "test_boost=%d/%d test_boost_interval=%d " "test_boost_duration=%d shutdown_secs=%d " - "onoff_interval=%d\n", + "onoff_interval=%d onoff_holdoff=%d\n", torture_type, tag, nrealreaders, nfakewriters, stat_interval, verbose, test_no_idle_hz, shuffle_interval, stutter, irqreader, fqs_duration, fqs_holdoff, fqs_stutter, test_boost, cur_ops->can_boost, test_boost_interval, test_boost_duration, shutdown_secs, - onoff_interval); + onoff_interval, onoff_holdoff); } static struct notifier_block rcutorture_shutdown_nb = { @@ -1410,6 +1413,11 @@ rcu_torture_onoff(void *arg) for_each_online_cpu(cpu) maxcpu = cpu; WARN_ON(maxcpu < 0); + if (onoff_holdoff > 0) { + VERBOSE_PRINTK_STRING("rcu_torture_onoff begin holdoff"); + schedule_timeout_interruptible(onoff_holdoff * HZ); + VERBOSE_PRINTK_STRING("rcu_torture_onoff end holdoff"); + } while (!kthread_should_stop()) { cpu = (rcu_random(&rand) >> 4) % (maxcpu + 1); if (cpu_online(cpu) && cpu_is_hotpluggable(cpu)) { -- cgit v1.2.3 From c13f3757d0fcdcc2b7fc5d5e38da76b8913e6648 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 20 Jan 2012 15:36:33 -0800 Subject: rcu: Add CPU-stall capability to rcutorture Add module parameters to rcutorture that induce a CPU stall. The stall_cpu parameter specifies how long to stall in seconds, defaulting to zero, which indicates no stalling is to be undertaken. The stall_cpu_holdoff parameter specifies how many seconds after insmod (or boot, if rcutorture is built into the kernel) that this stall is to start. The default value for stall_cpu_holdoff is ten seconds. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- Documentation/RCU/torture.txt | 18 ++++++++++++ kernel/rcutorture.c | 66 +++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 84 insertions(+) (limited to 'kernel') diff --git a/Documentation/RCU/torture.txt b/Documentation/RCU/torture.txt index d25be872ae33..375d3fb71437 100644 --- a/Documentation/RCU/torture.txt +++ b/Documentation/RCU/torture.txt @@ -86,6 +86,24 @@ shutdown_secs The number of seconds to run the test before terminating zero, which disables test termination and system shutdown. This capability is useful for automated testing. +stall_cpu The number of seconds that a CPU should be stalled while + within both an rcu_read_lock() and a preempt_disable(). + This stall happens only once per rcutorture run. + If you need multiple stalls, use modprobe and rmmod to + repeatedly run rcutorture. The default for stall_cpu + is zero, which prevents rcutorture from stalling a CPU. + + Note that attempts to rmmod rcutorture while the stall + is ongoing will hang, so be careful what value you + choose for this module parameter! In addition, too-large + values for stall_cpu might well induce failures and + warnings in other parts of the kernel. You have been + warned! + +stall_cpu_holdoff + The number of seconds to wait after rcutorture starts + before stalling a CPU. Defaults to 10 seconds. + stat_interval The number of seconds between output of torture statistics (via printk()). Regardless of the interval, statistics are printed when the module is unloaded. diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c index 2914cafe171b..5cfa23be43bd 100644 --- a/kernel/rcutorture.c +++ b/kernel/rcutorture.c @@ -67,6 +67,8 @@ static int fqs_stutter = 3; /* Wait time between bursts (s). */ static int onoff_interval; /* Wait time between CPU hotplugs, 0=disable. */ static int onoff_holdoff; /* Seconds after boot before CPU hotplugs. */ static int shutdown_secs; /* Shutdown time (s). <=0 for no shutdown. */ +static int stall_cpu; /* CPU-stall duration (s). 0 for no stall. */ +static int stall_cpu_holdoff = 10; /* Time to wait until stall (s). */ static int test_boost = 1; /* Test RCU prio boost: 0=no, 1=maybe, 2=yes. */ static int test_boost_interval = 7; /* Interval between boost tests, seconds. */ static int test_boost_duration = 4; /* Duration of each boost test, seconds. */ @@ -100,6 +102,10 @@ module_param(onoff_holdoff, int, 0444); MODULE_PARM_DESC(onoff_holdoff, "Time after boot before CPU hotplugs (s)"); module_param(shutdown_secs, int, 0444); MODULE_PARM_DESC(shutdown_secs, "Shutdown time (s), zero to disable."); +module_param(stall_cpu, int, 0444); +MODULE_PARM_DESC(stall_cpu, "Stall duration (s), zero to disable."); +module_param(stall_cpu_holdoff, int, 0444); +MODULE_PARM_DESC(stall_cpu_holdoff, "Time to wait before starting stall (s)."); module_param(test_boost, int, 0444); MODULE_PARM_DESC(test_boost, "Test RCU prio boost: 0=no, 1=maybe, 2=yes."); module_param(test_boost_interval, int, 0444); @@ -132,6 +138,7 @@ static struct task_struct *shutdown_task; #ifdef CONFIG_HOTPLUG_CPU static struct task_struct *onoff_task; #endif /* #ifdef CONFIG_HOTPLUG_CPU */ +static struct task_struct *stall_task; #define RCU_TORTURE_PIPE_LEN 10 @@ -1489,6 +1496,63 @@ static void rcu_torture_onoff_cleanup(void) #endif /* #else #ifdef CONFIG_HOTPLUG_CPU */ +/* + * CPU-stall kthread. It waits as specified by stall_cpu_holdoff, then + * induces a CPU stall for the time specified by stall_cpu. + */ +static int __cpuinit rcu_torture_stall(void *args) +{ + unsigned long stop_at; + + VERBOSE_PRINTK_STRING("rcu_torture_stall task started"); + if (stall_cpu_holdoff > 0) { + VERBOSE_PRINTK_STRING("rcu_torture_stall begin holdoff"); + schedule_timeout_interruptible(stall_cpu_holdoff * HZ); + VERBOSE_PRINTK_STRING("rcu_torture_stall end holdoff"); + } + if (!kthread_should_stop()) { + stop_at = get_seconds() + stall_cpu; + /* RCU CPU stall is expected behavior in following code. */ + printk(KERN_ALERT "rcu_torture_stall start.\n"); + rcu_read_lock(); + preempt_disable(); + while (ULONG_CMP_LT(get_seconds(), stop_at)) + continue; /* Induce RCU CPU stall warning. */ + preempt_enable(); + rcu_read_unlock(); + printk(KERN_ALERT "rcu_torture_stall end.\n"); + } + rcutorture_shutdown_absorb("rcu_torture_stall"); + while (!kthread_should_stop()) + schedule_timeout_interruptible(10 * HZ); + return 0; +} + +/* Spawn CPU-stall kthread, if stall_cpu specified. */ +static int __init rcu_torture_stall_init(void) +{ + int ret; + + if (stall_cpu <= 0) + return 0; + stall_task = kthread_run(rcu_torture_stall, NULL, "rcu_torture_stall"); + if (IS_ERR(stall_task)) { + ret = PTR_ERR(stall_task); + stall_task = NULL; + return ret; + } + return 0; +} + +/* Clean up after the CPU-stall kthread, if one was spawned. */ +static void rcu_torture_stall_cleanup(void) +{ + if (stall_task == NULL) + return; + VERBOSE_PRINTK_STRING("Stopping rcu_torture_stall_task."); + kthread_stop(stall_task); +} + static int rcutorture_cpu_notify(struct notifier_block *self, unsigned long action, void *hcpu) { @@ -1531,6 +1595,7 @@ rcu_torture_cleanup(void) fullstop = FULLSTOP_RMMOD; mutex_unlock(&fullstop_mutex); unregister_reboot_notifier(&rcutorture_shutdown_nb); + rcu_torture_stall_cleanup(); if (stutter_task) { VERBOSE_PRINTK_STRING("Stopping rcu_torture_stutter task"); kthread_stop(stutter_task); @@ -1831,6 +1896,7 @@ rcu_torture_init(void) } rcu_torture_onoff_init(); register_reboot_notifier(&rcutorture_shutdown_nb); + rcu_torture_stall_init(); rcutorture_record_test_transition(); mutex_unlock(&fullstop_mutex); return 0; -- cgit v1.2.3 From c0d6d01bffdce19fa19baad6cb8cc3eed7bfd6f5 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 23 Jan 2012 12:41:26 -0800 Subject: rcu: Check for illegal use of RCU from offlined CPUs Although it is legal to use RCU during early boot, it is anything but legal to use RCU at runtime from an offlined CPU. After all, RCU explicitly ignores offlined CPUs. This commit therefore adds checks for runtime use of RCU from offlined CPUs. These checks are not perfect, in particular, they can be subverted through use of things like rcu_dereference_raw(). Note that it is not possible to put checks in rcu_read_lock() and friends due to the fact that these primitives are used in code that might be used under either RCU or lock-based protection, which means that checking rcu_read_lock() gets you fat piles of false positives. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- include/linux/rcupdate.h | 19 +++++++++++++++++++ include/linux/srcu.h | 11 +++++++---- kernel/rcupdate.c | 5 +++++ kernel/rcutree.c | 29 +++++++++++++++++++++++++++++ kernel/rcutree_plugin.h | 1 + 5 files changed, 61 insertions(+), 4 deletions(-) (limited to 'kernel') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index f409529ff35a..146d37d31778 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -226,6 +226,15 @@ static inline void destroy_rcu_head_on_stack(struct rcu_head *head) } #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ +#if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) +bool rcu_lockdep_current_cpu_online(void); +#else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ +static inline bool rcu_lockdep_current_cpu_online(void) +{ + return 1; +} +#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ + #ifdef CONFIG_DEBUG_LOCK_ALLOC #ifdef CONFIG_PROVE_RCU @@ -270,6 +279,9 @@ extern int debug_lockdep_rcu_enabled(void); * occur in the same context, for example, it is illegal to invoke * rcu_read_unlock() in process context if the matching rcu_read_lock() * was invoked from within an irq handler. + * + * Note that rcu_read_lock() is disallowed if the CPU is either idle or + * offline from an RCU perspective, so check for those as well. */ static inline int rcu_read_lock_held(void) { @@ -277,6 +289,8 @@ static inline int rcu_read_lock_held(void) return 1; if (rcu_is_cpu_idle()) return 0; + if (!rcu_lockdep_current_cpu_online()) + return 0; return lock_is_held(&rcu_lock_map); } @@ -313,6 +327,9 @@ extern int rcu_read_lock_bh_held(void); * notice an extended quiescent state to other CPUs that started a grace * period. Otherwise we would delay any grace period as long as we run in * the idle task. + * + * Similarly, we avoid claiming an SRCU read lock held if the current + * CPU is offline. */ #ifdef CONFIG_PREEMPT_COUNT static inline int rcu_read_lock_sched_held(void) @@ -323,6 +340,8 @@ static inline int rcu_read_lock_sched_held(void) return 1; if (rcu_is_cpu_idle()) return 0; + if (!rcu_lockdep_current_cpu_online()) + return 0; if (debug_locks) lockdep_opinion = lock_is_held(&rcu_sched_lock_map); return lockdep_opinion || preempt_count() != 0 || irqs_disabled(); diff --git a/include/linux/srcu.h b/include/linux/srcu.h index e1b005918bbb..9a323728e60c 100644 --- a/include/linux/srcu.h +++ b/include/linux/srcu.h @@ -99,15 +99,18 @@ long srcu_batches_completed(struct srcu_struct *sp); * power mode. This way we can notice an extended quiescent state to * other CPUs that started a grace period. Otherwise we would delay any * grace period as long as we run in the idle task. + * + * Similarly, we avoid claiming an SRCU read lock held if the current + * CPU is offline. */ static inline int srcu_read_lock_held(struct srcu_struct *sp) { - if (rcu_is_cpu_idle()) - return 0; - if (!debug_lockdep_rcu_enabled()) return 1; - + if (rcu_is_cpu_idle()) + return 0; + if (!rcu_lockdep_current_cpu_online()) + return 0; return lock_is_held(&sp->dep_map); } diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index 2bc4e135ff23..a86f1741cc27 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -88,6 +88,9 @@ EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled); * section. * * Check debug_lockdep_rcu_enabled() to prevent false positives during boot. + * + * Note that rcu_read_lock() is disallowed if the CPU is either idle or + * offline from an RCU perspective, so check for those as well. */ int rcu_read_lock_bh_held(void) { @@ -95,6 +98,8 @@ int rcu_read_lock_bh_held(void) return 1; if (rcu_is_cpu_idle()) return 0; + if (!rcu_lockdep_current_cpu_online()) + return 0; return in_softirq() || irqs_disabled(); } EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held); diff --git a/kernel/rcutree.c b/kernel/rcutree.c index dccd2f78db4e..bcf7db2f2fd2 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -591,6 +591,35 @@ int rcu_is_cpu_idle(void) } EXPORT_SYMBOL(rcu_is_cpu_idle); +#ifdef CONFIG_HOTPLUG_CPU + +/* + * Is the current CPU online? Disable preemption to avoid false positives + * that could otherwise happen due to the current CPU number being sampled, + * this task being preempted, its old CPU being taken offline, resuming + * on some other CPU, then determining that its old CPU is now offline. + * It is OK to use RCU on an offline processor during initial boot, hence + * the check for rcu_scheduler_fully_active. + * + * Disable checking if in an NMI handler because we cannot safely report + * errors from NMI handlers anyway. + */ +bool rcu_lockdep_current_cpu_online(void) +{ + bool ret; + + if (in_nmi()) + return 1; + preempt_disable(); + ret = cpu_online(smp_processor_id()) || + !rcu_scheduler_fully_active; + preempt_enable(); + return ret; +} +EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online); + +#endif /* #ifdef CONFIG_HOTPLUG_CPU */ + #endif /* #ifdef CONFIG_PROVE_RCU */ /** diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index aa93b074bb2f..cecea84f4f3f 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -1946,6 +1946,7 @@ void synchronize_sched_expedited(void) /* Note that atomic_inc_return() implies full memory barrier. */ firstsnap = snap = atomic_inc_return(&sync_sched_expedited_started); get_online_cpus(); + WARN_ON_ONCE(cpu_is_offline(smp_processor_id())); /* * Each pass through the following loop attempts to force a -- cgit v1.2.3 From 3d3b7db0a22085cfc05c3318b9874f7fb8266d18 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 23 Jan 2012 17:05:46 -0800 Subject: rcu: Move synchronize_sched_expedited() to rcutree.c Now that TREE_RCU and TREE_PREEMPT_RCU no longer do anything different for the single-CPU case, there is no need for multiple definitions of synchronize_sched_expedited(). It is no longer in any sense a plug-in, so move it from kernel/rcutree_plugin.h to kernel/rcutree.c. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 117 ++++++++++++++++++++++++++++++++++++++++++++++++ kernel/rcutree_plugin.h | 116 ----------------------------------------------- 2 files changed, 117 insertions(+), 116 deletions(-) (limited to 'kernel') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index bcf7db2f2fd2..05470d4caba3 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -50,6 +50,8 @@ #include #include #include +#include +#include #include "rcutree.h" #include @@ -1918,6 +1920,121 @@ void synchronize_rcu_bh(void) } EXPORT_SYMBOL_GPL(synchronize_rcu_bh); +static atomic_t sync_sched_expedited_started = ATOMIC_INIT(0); +static atomic_t sync_sched_expedited_done = ATOMIC_INIT(0); + +static int synchronize_sched_expedited_cpu_stop(void *data) +{ + /* + * There must be a full memory barrier on each affected CPU + * between the time that try_stop_cpus() is called and the + * time that it returns. + * + * In the current initial implementation of cpu_stop, the + * above condition is already met when the control reaches + * this point and the following smp_mb() is not strictly + * necessary. Do smp_mb() anyway for documentation and + * robustness against future implementation changes. + */ + smp_mb(); /* See above comment block. */ + return 0; +} + +/* + * Wait for an rcu-sched grace period to elapse, but use "big hammer" + * approach to force grace period to end quickly. This consumes + * significant time on all CPUs, and is thus not recommended for + * any sort of common-case code. + * + * Note that it is illegal to call this function while holding any + * lock that is acquired by a CPU-hotplug notifier. Failing to + * observe this restriction will result in deadlock. + * + * This implementation can be thought of as an application of ticket + * locking to RCU, with sync_sched_expedited_started and + * sync_sched_expedited_done taking on the roles of the halves + * of the ticket-lock word. Each task atomically increments + * sync_sched_expedited_started upon entry, snapshotting the old value, + * then attempts to stop all the CPUs. If this succeeds, then each + * CPU will have executed a context switch, resulting in an RCU-sched + * grace period. We are then done, so we use atomic_cmpxchg() to + * update sync_sched_expedited_done to match our snapshot -- but + * only if someone else has not already advanced past our snapshot. + * + * On the other hand, if try_stop_cpus() fails, we check the value + * of sync_sched_expedited_done. If it has advanced past our + * initial snapshot, then someone else must have forced a grace period + * some time after we took our snapshot. In this case, our work is + * done for us, and we can simply return. Otherwise, we try again, + * but keep our initial snapshot for purposes of checking for someone + * doing our work for us. + * + * If we fail too many times in a row, we fall back to synchronize_sched(). + */ +void synchronize_sched_expedited(void) +{ + int firstsnap, s, snap, trycount = 0; + + /* Note that atomic_inc_return() implies full memory barrier. */ + firstsnap = snap = atomic_inc_return(&sync_sched_expedited_started); + get_online_cpus(); + WARN_ON_ONCE(cpu_is_offline(smp_processor_id())); + + /* + * Each pass through the following loop attempts to force a + * context switch on each CPU. + */ + while (try_stop_cpus(cpu_online_mask, + synchronize_sched_expedited_cpu_stop, + NULL) == -EAGAIN) { + put_online_cpus(); + + /* No joy, try again later. Or just synchronize_sched(). */ + if (trycount++ < 10) + udelay(trycount * num_online_cpus()); + else { + synchronize_sched(); + return; + } + + /* Check to see if someone else did our work for us. */ + s = atomic_read(&sync_sched_expedited_done); + if (UINT_CMP_GE((unsigned)s, (unsigned)firstsnap)) { + smp_mb(); /* ensure test happens before caller kfree */ + return; + } + + /* + * Refetching sync_sched_expedited_started allows later + * callers to piggyback on our grace period. We subtract + * 1 to get the same token that the last incrementer got. + * We retry after they started, so our grace period works + * for them, and they started after our first try, so their + * grace period works for us. + */ + get_online_cpus(); + snap = atomic_read(&sync_sched_expedited_started); + smp_mb(); /* ensure read is before try_stop_cpus(). */ + } + + /* + * Everyone up to our most recent fetch is covered by our grace + * period. Update the counter, but only if our work is still + * relevant -- which it won't be if someone who started later + * than we did beat us to the punch. + */ + do { + s = atomic_read(&sync_sched_expedited_done); + if (UINT_CMP_GE((unsigned)s, (unsigned)snap)) { + smp_mb(); /* ensure test happens before caller kfree */ + break; + } + } while (atomic_cmpxchg(&sync_sched_expedited_done, s, snap) != s); + + put_online_cpus(); +} +EXPORT_SYMBOL_GPL(synchronize_sched_expedited); + /* * Check to see if there is any immediate RCU-related work to be done * by the current CPU, for the specified type of RCU, returning 1 if so. diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index cecea84f4f3f..98ce17cf1fb5 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -25,7 +25,6 @@ */ #include -#include #define RCU_KTHREAD_PRIO 1 @@ -1888,121 +1887,6 @@ static void __cpuinit rcu_prepare_kthreads(int cpu) #endif /* #else #ifdef CONFIG_RCU_BOOST */ -static atomic_t sync_sched_expedited_started = ATOMIC_INIT(0); -static atomic_t sync_sched_expedited_done = ATOMIC_INIT(0); - -static int synchronize_sched_expedited_cpu_stop(void *data) -{ - /* - * There must be a full memory barrier on each affected CPU - * between the time that try_stop_cpus() is called and the - * time that it returns. - * - * In the current initial implementation of cpu_stop, the - * above condition is already met when the control reaches - * this point and the following smp_mb() is not strictly - * necessary. Do smp_mb() anyway for documentation and - * robustness against future implementation changes. - */ - smp_mb(); /* See above comment block. */ - return 0; -} - -/* - * Wait for an rcu-sched grace period to elapse, but use "big hammer" - * approach to force grace period to end quickly. This consumes - * significant time on all CPUs, and is thus not recommended for - * any sort of common-case code. - * - * Note that it is illegal to call this function while holding any - * lock that is acquired by a CPU-hotplug notifier. Failing to - * observe this restriction will result in deadlock. - * - * This implementation can be thought of as an application of ticket - * locking to RCU, with sync_sched_expedited_started and - * sync_sched_expedited_done taking on the roles of the halves - * of the ticket-lock word. Each task atomically increments - * sync_sched_expedited_started upon entry, snapshotting the old value, - * then attempts to stop all the CPUs. If this succeeds, then each - * CPU will have executed a context switch, resulting in an RCU-sched - * grace period. We are then done, so we use atomic_cmpxchg() to - * update sync_sched_expedited_done to match our snapshot -- but - * only if someone else has not already advanced past our snapshot. - * - * On the other hand, if try_stop_cpus() fails, we check the value - * of sync_sched_expedited_done. If it has advanced past our - * initial snapshot, then someone else must have forced a grace period - * some time after we took our snapshot. In this case, our work is - * done for us, and we can simply return. Otherwise, we try again, - * but keep our initial snapshot for purposes of checking for someone - * doing our work for us. - * - * If we fail too many times in a row, we fall back to synchronize_sched(). - */ -void synchronize_sched_expedited(void) -{ - int firstsnap, s, snap, trycount = 0; - - /* Note that atomic_inc_return() implies full memory barrier. */ - firstsnap = snap = atomic_inc_return(&sync_sched_expedited_started); - get_online_cpus(); - WARN_ON_ONCE(cpu_is_offline(smp_processor_id())); - - /* - * Each pass through the following loop attempts to force a - * context switch on each CPU. - */ - while (try_stop_cpus(cpu_online_mask, - synchronize_sched_expedited_cpu_stop, - NULL) == -EAGAIN) { - put_online_cpus(); - - /* No joy, try again later. Or just synchronize_sched(). */ - if (trycount++ < 10) - udelay(trycount * num_online_cpus()); - else { - synchronize_sched(); - return; - } - - /* Check to see if someone else did our work for us. */ - s = atomic_read(&sync_sched_expedited_done); - if (UINT_CMP_GE((unsigned)s, (unsigned)firstsnap)) { - smp_mb(); /* ensure test happens before caller kfree */ - return; - } - - /* - * Refetching sync_sched_expedited_started allows later - * callers to piggyback on our grace period. We subtract - * 1 to get the same token that the last incrementer got. - * We retry after they started, so our grace period works - * for them, and they started after our first try, so their - * grace period works for us. - */ - get_online_cpus(); - snap = atomic_read(&sync_sched_expedited_started); - smp_mb(); /* ensure read is before try_stop_cpus(). */ - } - - /* - * Everyone up to our most recent fetch is covered by our grace - * period. Update the counter, but only if our work is still - * relevant -- which it won't be if someone who started later - * than we did beat us to the punch. - */ - do { - s = atomic_read(&sync_sched_expedited_done); - if (UINT_CMP_GE((unsigned)s, (unsigned)snap)) { - smp_mb(); /* ensure test happens before caller kfree */ - break; - } - } while (atomic_cmpxchg(&sync_sched_expedited_done, s, snap) != s); - - put_online_cpus(); -} -EXPORT_SYMBOL_GPL(synchronize_sched_expedited); - #if !defined(CONFIG_RCU_FAST_NO_HZ) /* -- cgit v1.2.3 From c0cfbbb0d4fca14b828a7635a59784adfba8989d Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 23 Jan 2012 17:23:35 -0800 Subject: rcu: No interrupt disabling for rcu_prepare_for_idle() The rcu_prepare_for_idle() function is always called with interrupts disabled, so there is no reason to disable interrupts again within rcu_prepare_for_idle(). Therefore, this commit removes all of the interrupt disabling, also removing a latent disabling-unbalance bug. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree_plugin.h | 18 +----------------- 1 file changed, 1 insertion(+), 17 deletions(-) (limited to 'kernel') diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 98ce17cf1fb5..5e25ee327ccb 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -2096,10 +2096,6 @@ static void rcu_cleanup_after_idle(int cpu) */ static void rcu_prepare_for_idle(int cpu) { - unsigned long flags; - - local_irq_save(flags); - /* * If there are no callbacks on this CPU, enter dyntick-idle mode. * Also reset state to avoid prejudicing later attempts. @@ -2107,7 +2103,6 @@ static void rcu_prepare_for_idle(int cpu) if (!rcu_cpu_has_callbacks(cpu)) { per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1; per_cpu(rcu_dyntick_drain, cpu) = 0; - local_irq_restore(flags); trace_rcu_prep_idle("No callbacks"); return; } @@ -2117,7 +2112,6 @@ static void rcu_prepare_for_idle(int cpu) * refrained from disabling the scheduling-clock tick. */ if (per_cpu(rcu_dyntick_holdoff, cpu) == jiffies) { - local_irq_restore(flags); trace_rcu_prep_idle("In holdoff"); return; } @@ -2142,7 +2136,6 @@ static void rcu_prepare_for_idle(int cpu) } else if (--per_cpu(rcu_dyntick_drain, cpu) <= 0) { /* We have hit the limit, so time to give up. */ per_cpu(rcu_dyntick_holdoff, cpu) = jiffies; - local_irq_restore(flags); trace_rcu_prep_idle("Begin holdoff"); invoke_rcu_core(); /* Force the CPU out of dyntick-idle. */ return; @@ -2154,23 +2147,17 @@ static void rcu_prepare_for_idle(int cpu) */ #ifdef CONFIG_TREE_PREEMPT_RCU if (per_cpu(rcu_preempt_data, cpu).nxtlist) { - local_irq_restore(flags); rcu_preempt_qs(cpu); force_quiescent_state(&rcu_preempt_state, 0); - local_irq_save(flags); } #endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */ if (per_cpu(rcu_sched_data, cpu).nxtlist) { - local_irq_restore(flags); rcu_sched_qs(cpu); force_quiescent_state(&rcu_sched_state, 0); - local_irq_save(flags); } if (per_cpu(rcu_bh_data, cpu).nxtlist) { - local_irq_restore(flags); rcu_bh_qs(cpu); force_quiescent_state(&rcu_bh_state, 0); - local_irq_save(flags); } /* @@ -2178,13 +2165,10 @@ static void rcu_prepare_for_idle(int cpu) * So try forcing the callbacks through the grace period. */ if (rcu_cpu_has_callbacks(cpu)) { - local_irq_restore(flags); trace_rcu_prep_idle("More callbacks"); invoke_rcu_core(); - } else { - local_irq_restore(flags); + } else trace_rcu_prep_idle("Callbacks drained"); - } } #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ -- cgit v1.2.3 From c5fdcec927ee31fc96e92339c3a83ac6e0725289 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 30 Jan 2012 08:46:32 -0800 Subject: lockdep: Add CPU-idle/offline warning to lockdep-RCU splat It is illegal to use RCU from a CPU that has reported idleness or offlinedness to RCU. However, it can be quite difficult to determine from a stack trace whether or not a given CPU is idle or offline. Therefore, this commit adds idle/offline diagnostics to the lockdep-RCU error message. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/lockdep.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) (limited to 'kernel') diff --git a/kernel/lockdep.c b/kernel/lockdep.c index 8889f7dd7c46..ea9ee4518c35 100644 --- a/kernel/lockdep.c +++ b/kernel/lockdep.c @@ -4176,7 +4176,13 @@ void lockdep_rcu_suspicious(const char *file, const int line, const char *s) printk("-------------------------------\n"); printk("%s:%d %s!\n", file, line, s); printk("\nother info that might help us debug this:\n\n"); - printk("\nrcu_scheduler_active = %d, debug_locks = %d\n", rcu_scheduler_active, debug_locks); + printk("\n%srcu_scheduler_active = %d, debug_locks = %d\n", + !rcu_lockdep_current_cpu_online() + ? "RCU used illegally from offline CPU!\n" + : rcu_is_cpu_idle() + ? "RCU used illegally from idle CPU!\n" + : "", + rcu_scheduler_active, debug_locks); /* * If a CPU is in the RCU-free window in idle (ie: in the section -- cgit v1.2.3 From 2036d94a7b61ca5032ce90f2bda06afec0fe713e Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 30 Jan 2012 17:02:47 -0800 Subject: rcu: Rework detection of use of RCU by offline CPUs Because newly offlined CPUs continue executing after completing the CPU_DYING notifiers, they legitimately enter the scheduler and use RCU while appearing to be offline. This calls for a more sophisticated approach as follows: 1. RCU marks the CPU online during the CPU_UP_PREPARE phase. 2. RCU marks the CPU offline during the CPU_DEAD phase. 3. Diagnostics regarding use of read-side RCU by offline CPUs use RCU's accounting rather than the cpu_online_map. (Note that __call_rcu() still uses cpu_online_map to detect illegal invocations within CPU_DYING notifiers.) 4. Offline CPUs are prevented from hanging the system by force_quiescent_state(), which pays attention to cpu_online_map. Some additional work (in a later commit) will be needed to guarantee that force_quiescent_state() waits a full jiffy before assuming that a CPU is offline, for example, when called from idle entry. (This commit also makes the one-jiffy wait explicit, since the old-style implicit wait can now be defeated by RCU_FAST_NO_HZ and by rcutorture.) This approach avoids the false positives encountered when attempting to use more exact classification of CPU online/offline state. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- Documentation/RCU/trace.txt | 36 +++++++------- kernel/rcutree.c | 113 ++++++++++++++++++++++++++------------------ kernel/rcutree.h | 1 - kernel/rcutree_plugin.h | 2 +- kernel/rcutree_trace.c | 6 +-- 5 files changed, 87 insertions(+), 71 deletions(-) (limited to 'kernel') diff --git a/Documentation/RCU/trace.txt b/Documentation/RCU/trace.txt index 49587abfc2f7..f6f15ce39903 100644 --- a/Documentation/RCU/trace.txt +++ b/Documentation/RCU/trace.txt @@ -33,23 +33,23 @@ rcu/rcuboost: The output of "cat rcu/rcudata" looks as follows: rcu_sched: - 0 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=545/1/0 df=50 of=0 ri=0 ql=163 qs=NRW. kt=0/W/0 ktl=ebc3 b=10 ci=153737 co=0 ca=0 - 1 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=967/1/0 df=58 of=0 ri=0 ql=634 qs=NRW. kt=0/W/1 ktl=58c b=10 ci=191037 co=0 ca=0 - 2 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=1081/1/0 df=175 of=0 ri=0 ql=74 qs=N.W. kt=0/W/2 ktl=da94 b=10 ci=75991 co=0 ca=0 - 3 c=20942 g=20943 pq=1 pgp=20942 qp=1 dt=1846/0/0 df=404 of=0 ri=0 ql=0 qs=.... kt=0/W/3 ktl=d1cd b=10 ci=72261 co=0 ca=0 - 4 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=369/1/0 df=83 of=0 ri=0 ql=48 qs=N.W. kt=0/W/4 ktl=e0e7 b=10 ci=128365 co=0 ca=0 - 5 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=381/1/0 df=64 of=0 ri=0 ql=169 qs=NRW. kt=0/W/5 ktl=fb2f b=10 ci=164360 co=0 ca=0 - 6 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=1037/1/0 df=183 of=0 ri=0 ql=62 qs=N.W. kt=0/W/6 ktl=d2ad b=10 ci=65663 co=0 ca=0 - 7 c=20897 g=20897 pq=1 pgp=20896 qp=0 dt=1572/0/0 df=382 of=0 ri=0 ql=0 qs=.... kt=0/W/7 ktl=cf15 b=10 ci=75006 co=0 ca=0 + 0 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=545/1/0 df=50 of=0 ql=163 qs=NRW. kt=0/W/0 ktl=ebc3 b=10 ci=153737 co=0 ca=0 + 1 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=967/1/0 df=58 of=0 ql=634 qs=NRW. kt=0/W/1 ktl=58c b=10 ci=191037 co=0 ca=0 + 2 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=1081/1/0 df=175 of=0 ql=74 qs=N.W. kt=0/W/2 ktl=da94 b=10 ci=75991 co=0 ca=0 + 3 c=20942 g=20943 pq=1 pgp=20942 qp=1 dt=1846/0/0 df=404 of=0 ql=0 qs=.... kt=0/W/3 ktl=d1cd b=10 ci=72261 co=0 ca=0 + 4 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=369/1/0 df=83 of=0 ql=48 qs=N.W. kt=0/W/4 ktl=e0e7 b=10 ci=128365 co=0 ca=0 + 5 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=381/1/0 df=64 of=0 ql=169 qs=NRW. kt=0/W/5 ktl=fb2f b=10 ci=164360 co=0 ca=0 + 6 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=1037/1/0 df=183 of=0 ql=62 qs=N.W. kt=0/W/6 ktl=d2ad b=10 ci=65663 co=0 ca=0 + 7 c=20897 g=20897 pq=1 pgp=20896 qp=0 dt=1572/0/0 df=382 of=0 ql=0 qs=.... kt=0/W/7 ktl=cf15 b=10 ci=75006 co=0 ca=0 rcu_bh: - 0 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=545/1/0 df=6 of=0 ri=1 ql=0 qs=.... kt=0/W/0 ktl=ebc3 b=10 ci=0 co=0 ca=0 - 1 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=967/1/0 df=3 of=0 ri=1 ql=0 qs=.... kt=0/W/1 ktl=58c b=10 ci=151 co=0 ca=0 - 2 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=1081/1/0 df=6 of=0 ri=1 ql=0 qs=.... kt=0/W/2 ktl=da94 b=10 ci=0 co=0 ca=0 - 3 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=1846/0/0 df=8 of=0 ri=1 ql=0 qs=.... kt=0/W/3 ktl=d1cd b=10 ci=0 co=0 ca=0 - 4 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=369/1/0 df=6 of=0 ri=1 ql=0 qs=.... kt=0/W/4 ktl=e0e7 b=10 ci=0 co=0 ca=0 - 5 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=381/1/0 df=4 of=0 ri=1 ql=0 qs=.... kt=0/W/5 ktl=fb2f b=10 ci=0 co=0 ca=0 - 6 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=1037/1/0 df=6 of=0 ri=1 ql=0 qs=.... kt=0/W/6 ktl=d2ad b=10 ci=0 co=0 ca=0 - 7 c=1474 g=1474 pq=1 pgp=1473 qp=0 dt=1572/0/0 df=8 of=0 ri=1 ql=0 qs=.... kt=0/W/7 ktl=cf15 b=10 ci=0 co=0 ca=0 + 0 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=545/1/0 df=6 of=0 ql=0 qs=.... kt=0/W/0 ktl=ebc3 b=10 ci=0 co=0 ca=0 + 1 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=967/1/0 df=3 of=0 ql=0 qs=.... kt=0/W/1 ktl=58c b=10 ci=151 co=0 ca=0 + 2 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=1081/1/0 df=6 of=0 ql=0 qs=.... kt=0/W/2 ktl=da94 b=10 ci=0 co=0 ca=0 + 3 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=1846/0/0 df=8 of=0 ql=0 qs=.... kt=0/W/3 ktl=d1cd b=10 ci=0 co=0 ca=0 + 4 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=369/1/0 df=6 of=0 ql=0 qs=.... kt=0/W/4 ktl=e0e7 b=10 ci=0 co=0 ca=0 + 5 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=381/1/0 df=4 of=0 ql=0 qs=.... kt=0/W/5 ktl=fb2f b=10 ci=0 co=0 ca=0 + 6 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=1037/1/0 df=6 of=0 ql=0 qs=.... kt=0/W/6 ktl=d2ad b=10 ci=0 co=0 ca=0 + 7 c=1474 g=1474 pq=1 pgp=1473 qp=0 dt=1572/0/0 df=8 of=0 ql=0 qs=.... kt=0/W/7 ktl=cf15 b=10 ci=0 co=0 ca=0 The first section lists the rcu_data structures for rcu_sched, the second for rcu_bh. Note that CONFIG_TREE_PREEMPT_RCU kernels will have an @@ -119,10 +119,6 @@ o "of" is the number of times that some other CPU has forced a CPU is offline when it is really alive and kicking) is a fatal error, so it makes sense to err conservatively. -o "ri" is the number of times that RCU has seen fit to send a - reschedule IPI to this CPU in order to get it to report a - quiescent state. - o "ql" is the number of RCU callbacks currently residing on this CPU. This is the total number of callbacks, regardless of what state they are in (new, waiting for grace period to diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 05470d4caba3..708469a06860 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -320,25 +320,18 @@ static struct rcu_node *rcu_get_root(struct rcu_state *rsp) static int rcu_implicit_offline_qs(struct rcu_data *rdp) { /* - * If the CPU is offline, it is in a quiescent state. We can - * trust its state not to change because interrupts are disabled. + * If the CPU is offline for more than a jiffy, it is in a quiescent + * state. We can trust its state not to change because interrupts + * are disabled. The reason for the jiffy's worth of slack is to + * handle CPUs initializing on the way up and finding their way + * to the idle loop on the way down. */ - if (cpu_is_offline(rdp->cpu)) { + if (cpu_is_offline(rdp->cpu) && + ULONG_CMP_LT(rdp->rsp->gp_start + 2, jiffies)) { trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, "ofl"); rdp->offline_fqs++; return 1; } - - /* - * The CPU is online, so send it a reschedule IPI. This forces - * it through the scheduler, and (inefficiently) also handles cases - * where idle loops fail to inform RCU about the CPU being idle. - */ - if (rdp->cpu != smp_processor_id()) - smp_send_reschedule(rdp->cpu); - else - set_need_resched(); - rdp->resched_ipi++; return 0; } @@ -601,19 +594,33 @@ EXPORT_SYMBOL(rcu_is_cpu_idle); * this task being preempted, its old CPU being taken offline, resuming * on some other CPU, then determining that its old CPU is now offline. * It is OK to use RCU on an offline processor during initial boot, hence - * the check for rcu_scheduler_fully_active. + * the check for rcu_scheduler_fully_active. Note also that it is OK + * for a CPU coming online to use RCU for one jiffy prior to marking itself + * online in the cpu_online_mask. Similarly, it is OK for a CPU going + * offline to continue to use RCU for one jiffy after marking itself + * offline in the cpu_online_mask. This leniency is necessary given the + * non-atomic nature of the online and offline processing, for example, + * the fact that a CPU enters the scheduler after completing the CPU_DYING + * notifiers. + * + * This is also why RCU internally marks CPUs online during the + * CPU_UP_PREPARE phase and offline during the CPU_DEAD phase. * * Disable checking if in an NMI handler because we cannot safely report * errors from NMI handlers anyway. */ bool rcu_lockdep_current_cpu_online(void) { + struct rcu_data *rdp; + struct rcu_node *rnp; bool ret; if (in_nmi()) return 1; preempt_disable(); - ret = cpu_online(smp_processor_id()) || + rdp = &__get_cpu_var(rcu_sched_data); + rnp = rdp->mynode; + ret = (rdp->grpmask & rnp->qsmaskinit) || !rcu_scheduler_fully_active; preempt_enable(); return ret; @@ -1308,14 +1315,12 @@ rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp) */ static void rcu_cleanup_dying_cpu(struct rcu_state *rsp) { - unsigned long flags; int i; unsigned long mask; - int need_report; int receive_cpu = cpumask_any(cpu_online_mask); struct rcu_data *rdp = this_cpu_ptr(rsp->rda); struct rcu_data *receive_rdp = per_cpu_ptr(rsp->rda, receive_cpu); - struct rcu_node *rnp = rdp->mynode; /* For dying CPU. */ + RCU_TRACE(struct rcu_node *rnp = rdp->mynode); /* For dying CPU. */ /* First, adjust the counts. */ if (rdp->nxtlist != NULL) { @@ -1381,32 +1386,6 @@ static void rcu_cleanup_dying_cpu(struct rcu_state *rsp) "cpuofl"); rcu_report_qs_rdp(smp_processor_id(), rsp, rdp, rsp->gpnum); /* Note that rcu_report_qs_rdp() might call trace_rcu_grace_period(). */ - - /* - * Remove the dying CPU from the bitmasks in the rcu_node - * hierarchy. Because we are in stop_machine() context, we - * automatically exclude ->onofflock critical sections. - */ - do { - raw_spin_lock_irqsave(&rnp->lock, flags); - rnp->qsmaskinit &= ~mask; - if (rnp->qsmaskinit != 0) { - raw_spin_unlock_irqrestore(&rnp->lock, flags); - break; - } - if (rnp == rdp->mynode) { - need_report = rcu_preempt_offline_tasks(rsp, rnp, rdp); - if (need_report & RCU_OFL_TASKS_NORM_GP) - rcu_report_unblock_qs_rnp(rnp, flags); - else - raw_spin_unlock_irqrestore(&rnp->lock, flags); - if (need_report & RCU_OFL_TASKS_EXP_GP) - rcu_report_exp_rnp(rsp, rnp, true); - } else - raw_spin_unlock_irqrestore(&rnp->lock, flags); - mask = rnp->grpmask; - rnp = rnp->parent; - } while (rnp != NULL); } /* @@ -1417,11 +1396,53 @@ static void rcu_cleanup_dying_cpu(struct rcu_state *rsp) */ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp) { + unsigned long flags; + unsigned long mask; + int need_report = 0; struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); - struct rcu_node *rnp = rdp->mynode; + struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rnp. */ + /* Adjust any no-longer-needed kthreads. */ rcu_stop_cpu_kthread(cpu); rcu_node_kthread_setaffinity(rnp, -1); + + /* Remove the dying CPU from the bitmasks in the rcu_node hierarchy. */ + + /* Exclude any attempts to start a new grace period. */ + raw_spin_lock_irqsave(&rsp->onofflock, flags); + + /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */ + mask = rdp->grpmask; /* rnp->grplo is constant. */ + do { + raw_spin_lock(&rnp->lock); /* irqs already disabled. */ + rnp->qsmaskinit &= ~mask; + if (rnp->qsmaskinit != 0) { + if (rnp != rdp->mynode) + raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ + break; + } + if (rnp == rdp->mynode) + need_report = rcu_preempt_offline_tasks(rsp, rnp, rdp); + else + raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ + mask = rnp->grpmask; + rnp = rnp->parent; + } while (rnp != NULL); + + /* + * We still hold the leaf rcu_node structure lock here, and + * irqs are still disabled. The reason for this subterfuge is + * because invoking rcu_report_unblock_qs_rnp() with ->onofflock + * held leads to deadlock. + */ + raw_spin_unlock(&rsp->onofflock); /* irqs remain disabled. */ + rnp = rdp->mynode; + if (need_report & RCU_OFL_TASKS_NORM_GP) + rcu_report_unblock_qs_rnp(rnp, flags); + else + raw_spin_unlock_irqrestore(&rnp->lock, flags); + if (need_report & RCU_OFL_TASKS_EXP_GP) + rcu_report_exp_rnp(rsp, rnp, true); } #else /* #ifdef CONFIG_HOTPLUG_CPU */ diff --git a/kernel/rcutree.h b/kernel/rcutree.h index e2ac8ee415bb..cdd1be0a4072 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -289,7 +289,6 @@ struct rcu_data { /* 4) reasons this CPU needed to be kicked by force_quiescent_state */ unsigned long dynticks_fqs; /* Kicked due to dynticks idle. */ unsigned long offline_fqs; /* Kicked due to being offline. */ - unsigned long resched_ipi; /* Sent a resched IPI. */ /* 5) __rcu_pending() statistics. */ unsigned long n_rcu_pending; /* rcu_pending() calls since boot. */ diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 5e25ee327ccb..07f880445d8d 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -610,7 +610,7 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp, * absolutely necessary, but this is a good performance/complexity * tradeoff. */ - if (rcu_preempt_blocked_readers_cgp(rnp)) + if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0) retval |= RCU_OFL_TASKS_NORM_GP; if (rcu_preempted_readers_exp(rnp)) retval |= RCU_OFL_TASKS_EXP_GP; diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c index db0987c1e1bd..ed459edeff43 100644 --- a/kernel/rcutree_trace.c +++ b/kernel/rcutree_trace.c @@ -72,7 +72,7 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp) rdp->dynticks->dynticks_nesting, rdp->dynticks->dynticks_nmi_nesting, rdp->dynticks_fqs); - seq_printf(m, " of=%lu ri=%lu", rdp->offline_fqs, rdp->resched_ipi); + seq_printf(m, " of=%lu", rdp->offline_fqs); seq_printf(m, " ql=%ld/%ld qs=%c%c%c%c", rdp->qlen_lazy, rdp->qlen, ".N"[rdp->nxttail[RCU_NEXT_READY_TAIL] != @@ -144,7 +144,7 @@ static void print_one_rcu_data_csv(struct seq_file *m, struct rcu_data *rdp) rdp->dynticks->dynticks_nesting, rdp->dynticks->dynticks_nmi_nesting, rdp->dynticks_fqs); - seq_printf(m, ",%lu,%lu", rdp->offline_fqs, rdp->resched_ipi); + seq_printf(m, ",%lu", rdp->offline_fqs); seq_printf(m, ",%ld,%ld,\"%c%c%c%c\"", rdp->qlen_lazy, rdp->qlen, ".N"[rdp->nxttail[RCU_NEXT_READY_TAIL] != rdp->nxttail[RCU_NEXT_TAIL]], @@ -168,7 +168,7 @@ static int show_rcudata_csv(struct seq_file *m, void *unused) { seq_puts(m, "\"CPU\",\"Online?\",\"c\",\"g\",\"pq\",\"pgp\",\"pq\","); seq_puts(m, "\"dt\",\"dt nesting\",\"dt NMI nesting\",\"df\","); - seq_puts(m, "\"of\",\"ri\",\"qll\",\"ql\",\"qs\""); + seq_puts(m, "\"of\",\"qll\",\"ql\",\"qs\""); #ifdef CONFIG_RCU_BOOST seq_puts(m, "\"kt\",\"ktl\""); #endif /* #ifdef CONFIG_RCU_BOOST */ -- cgit v1.2.3 From 236fefafe5d3d34b78ed2ccf5510909716112326 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 31 Jan 2012 14:00:41 -0800 Subject: rcu: Call out dangers of expedited RCU primitives The expedited RCU primitives can be quite useful, but they have some high costs as well. This commit updates and creates docbook comments calling out the costs, and updates the RCU documentation as well. Signed-off-by: Paul E. McKenney --- Documentation/RCU/checklist.txt | 14 ++++++++++++++ include/linux/rcutree.h | 16 ++++++++++++++++ kernel/rcutree.c | 22 ++++++++++++++-------- kernel/rcutree_plugin.h | 20 ++++++++++++++++---- kernel/srcu.c | 27 +++++++++++++++++---------- 5 files changed, 77 insertions(+), 22 deletions(-) (limited to 'kernel') diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt index bff2d8be1e18..5c8d74968090 100644 --- a/Documentation/RCU/checklist.txt +++ b/Documentation/RCU/checklist.txt @@ -180,6 +180,20 @@ over a rather long period of time, but improvements are always welcome! operations that would not normally be undertaken while a real-time workload is running. + In particular, if you find yourself invoking one of the expedited + primitives repeatedly in a loop, please do everyone a favor: + Restructure your code so that it batches the updates, allowing + a single non-expedited primitive to cover the entire batch. + This will very likely be faster than the loop containing the + expedited primitive, and will be much much easier on the rest + of the system, especially to real-time workloads running on + the rest of the system. + + In addition, it is illegal to call the expedited forms from + a CPU-hotplug notifier, or while holding a lock that is acquired + by a CPU-hotplug notifier. Failing to observe this restriction + will result in deadlock. + 7. If the updater uses call_rcu() or synchronize_rcu(), then the corresponding readers must use rcu_read_lock() and rcu_read_unlock(). If the updater uses call_rcu_bh() or diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index 73892483fd05..e8ee5dd0854c 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -63,6 +63,22 @@ extern void synchronize_rcu_expedited(void); void kfree_call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)); +/** + * synchronize_rcu_bh_expedited - Brute-force RCU-bh grace period + * + * Wait for an RCU-bh grace period to elapse, but use a "big hammer" + * approach to force the grace period to end quickly. This consumes + * significant time on all CPUs and is unfriendly to real-time workloads, + * so is thus not recommended for any sort of common-case code. In fact, + * if you are using synchronize_rcu_bh_expedited() in a loop, please + * restructure your code to batch your updates, and then use a single + * synchronize_rcu_bh() instead. + * + * Note that it is illegal to call this function while holding any lock + * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal + * to call this function from a CPU-hotplug notifier. Failing to observe + * these restriction will result in deadlock. + */ static inline void synchronize_rcu_bh_expedited(void) { synchronize_sched_expedited(); diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 708469a06860..df0e3c1bb68e 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1961,15 +1961,21 @@ static int synchronize_sched_expedited_cpu_stop(void *data) return 0; } -/* - * Wait for an rcu-sched grace period to elapse, but use "big hammer" - * approach to force grace period to end quickly. This consumes - * significant time on all CPUs, and is thus not recommended for - * any sort of common-case code. +/** + * synchronize_sched_expedited - Brute-force RCU-sched grace period + * + * Wait for an RCU-sched grace period to elapse, but use a "big hammer" + * approach to force the grace period to end quickly. This consumes + * significant time on all CPUs and is unfriendly to real-time workloads, + * so is thus not recommended for any sort of common-case code. In fact, + * if you are using synchronize_sched_expedited() in a loop, please + * restructure your code to batch your updates, and then use a single + * synchronize_sched() instead. * - * Note that it is illegal to call this function while holding any - * lock that is acquired by a CPU-hotplug notifier. Failing to - * observe this restriction will result in deadlock. + * Note that it is illegal to call this function while holding any lock + * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal + * to call this function from a CPU-hotplug notifier. Failing to observe + * these restriction will result in deadlock. * * This implementation can be thought of as an application of ticket * locking to RCU, with sync_sched_expedited_started and diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 07f880445d8d..f7ceadf4986e 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -835,10 +835,22 @@ sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp) rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */ } -/* - * Wait for an rcu-preempt grace period, but expedite it. The basic idea - * is to invoke synchronize_sched_expedited() to push all the tasks to - * the ->blkd_tasks lists and wait for this list to drain. +/** + * synchronize_rcu_expedited - Brute-force RCU grace period + * + * Wait for an RCU-preempt grace period, but expedite it. The basic + * idea is to invoke synchronize_sched_expedited() to push all the tasks to + * the ->blkd_tasks lists and wait for this list to drain. This consumes + * significant time on all CPUs and is unfriendly to real-time workloads, + * so is thus not recommended for any sort of common-case code. + * In fact, if you are using synchronize_rcu_expedited() in a loop, + * please restructure your code to batch your updates, and then Use a + * single synchronize_rcu() instead. + * + * Note that it is illegal to call this function while holding any lock + * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal + * to call this function from a CPU-hotplug notifier. Failing to observe + * these restriction will result in deadlock. */ void synchronize_rcu_expedited(void) { diff --git a/kernel/srcu.c b/kernel/srcu.c index 3f99fa0e8ed3..ba35f3a4a1f4 100644 --- a/kernel/srcu.c +++ b/kernel/srcu.c @@ -286,19 +286,26 @@ void synchronize_srcu(struct srcu_struct *sp) EXPORT_SYMBOL_GPL(synchronize_srcu); /** - * synchronize_srcu_expedited - like synchronize_srcu, but less patient + * synchronize_srcu_expedited - Brute-force SRCU grace period * @sp: srcu_struct with which to synchronize. * - * Flip the completed counter, and wait for the old count to drain to zero. - * As with classic RCU, the updater must use some separate means of - * synchronizing concurrent updates. Can block; must be called from - * process context. + * Wait for an SRCU grace period to elapse, but use a "big hammer" + * approach to force the grace period to end quickly. This consumes + * significant time on all CPUs and is unfriendly to real-time workloads, + * so is thus not recommended for any sort of common-case code. In fact, + * if you are using synchronize_srcu_expedited() in a loop, please + * restructure your code to batch your updates, and then use a single + * synchronize_srcu() instead. * - * Note that it is illegal to call synchronize_srcu_expedited() - * from the corresponding SRCU read-side critical section; doing so - * will result in deadlock. However, it is perfectly legal to call - * synchronize_srcu_expedited() on one srcu_struct from some other - * srcu_struct's read-side critical section. + * Note that it is illegal to call this function while holding any lock + * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal + * to call this function from a CPU-hotplug notifier. Failing to observe + * these restriction will result in deadlock. It is also illegal to call + * synchronize_srcu_expedited() from the corresponding SRCU read-side + * critical section; doing so will result in deadlock. However, it is + * perfectly legal to call synchronize_srcu_expedited() on one srcu_struct + * from some other srcu_struct's read-side critical section, as long as + * the resulting graph of srcu_structs is acyclic. */ void synchronize_srcu_expedited(struct srcu_struct *sp) { -- cgit v1.2.3 From 7129d383d9f46eb8276bee5fb46df63f09a70130 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 31 Jan 2012 16:46:34 -0800 Subject: rcu: Trace only after NULL-pointer check Fix a bonehead error introduced when adding event tracing to rcutorture. Move the traces to follow the NULL-pointer checks. Signed-off-by: Paul E. McKenney --- kernel/rcutorture.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'kernel') diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c index 5cfa23be43bd..ed1c72bd9c09 100644 --- a/kernel/rcutorture.c +++ b/kernel/rcutorture.c @@ -1000,12 +1000,12 @@ static void rcu_torture_timer(unsigned long unused) rcu_read_lock_bh_held() || rcu_read_lock_sched_held() || srcu_read_lock_held(&srcu_ctl)); - do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu); if (p == NULL) { /* Leave because rcu_torture_writer is not yet underway */ cur_ops->readunlock(idx); return; } + do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu); if (p->rtort_mbtest == 0) atomic_inc(&n_rcu_torture_mberror); spin_lock(&rand_lock); @@ -1063,13 +1063,13 @@ rcu_torture_reader(void *arg) rcu_read_lock_bh_held() || rcu_read_lock_sched_held() || srcu_read_lock_held(&srcu_ctl)); - do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu); if (p == NULL) { /* Wait for rcu_torture_writer to get underway */ cur_ops->readunlock(idx); schedule_timeout_interruptible(HZ); continue; } + do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu); if (p->rtort_mbtest == 0) atomic_inc(&n_rcu_torture_mberror); cur_ops->read_delay(&rand); -- cgit v1.2.3 From 3c1b1ce00d2702d6be9b92233822e560f37ea780 Mon Sep 17 00:00:00 2001 From: Julia Lawall Date: Thu, 2 Feb 2012 07:52:54 -0800 Subject: PTR_ERR should be called before its argument is cleared. The semantic match that finds this problem is as follows: (http://coccinelle.lip6.fr/) // @@ expression e,e1; constant c; @@ *e = c ... when != e = e1 when != &e when != true IS_ERR(e) *PTR_ERR(e) // Signed-off-by: Julia Lawall Reported-by: Josh Triplett Signed-off-by: Paul E. McKenney --- kernel/rcutorture.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) (limited to 'kernel') diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c index ed1c72bd9c09..a89b381a8c6e 100644 --- a/kernel/rcutorture.c +++ b/kernel/rcutorture.c @@ -1465,12 +1465,15 @@ rcu_torture_onoff(void *arg) static int __cpuinit rcu_torture_onoff_init(void) { + int ret; + if (onoff_interval <= 0) return 0; onoff_task = kthread_run(rcu_torture_onoff, NULL, "rcu_torture_onoff"); if (IS_ERR(onoff_task)) { + ret = PTR_ERR(onoff_task); onoff_task = NULL; - return PTR_ERR(onoff_task); + return ret; } return 0; } -- cgit v1.2.3 From ce5df97be530e4746bf9a4ac14589a1cfdfd8efc Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 2 Feb 2012 08:26:06 -0800 Subject: rcu: Remove redundant check for rcu_head misalignment There is now an unconditional check for rcu_head misalignment in __call_rcu(), so remove the old conditional one in debug_rcu_head_queue(). Reported-by: Josh Triplett Signed-off-by: Paul E. McKenney --- kernel/rcu.h | 1 - 1 file changed, 1 deletion(-) (limited to 'kernel') diff --git a/kernel/rcu.h b/kernel/rcu.h index a074b0b43fc2..30876f4063b6 100644 --- a/kernel/rcu.h +++ b/kernel/rcu.h @@ -50,7 +50,6 @@ extern struct debug_obj_descr rcuhead_debug_descr; static inline void debug_rcu_head_queue(struct rcu_head *head) { - WARN_ON_ONCE((unsigned long)head & 0x3); debug_object_activate(head, &rcuhead_debug_descr); debug_object_active_state(head, &rcuhead_debug_descr, STATE_RCU_HEAD_READY, -- cgit v1.2.3 From 29e37d814188ac8d60f2120583704d3ef6d634b4 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 17 Nov 2011 16:55:56 -0800 Subject: rcu: Allow nesting of rcu_idle_enter() and rcu_idle_exit() Use of RCU in the idle loop is incorrect, quite a few instances of just that have made their way into mainline, primarily event tracing. The problem with RCU read-side critical sections on CPUs that RCU believes to be idle is that RCU is completely ignoring the CPU, along with any attempts and RCU read-side critical sections. The approaches of eliminating the offending uses and of pushing the definition of idle down beyond the offending uses have both proved impractical. The new approach is to encapsulate offending uses of RCU with rcu_idle_exit() and rcu_idle_enter(), but this requires nesting for code that is invoked both during idle and and during normal execution. Therefore, this commit modifies rcu_idle_enter() and rcu_idle_exit() to permit nesting. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett Acked-by: Deepthi Dharwar --- kernel/rcu.h | 21 ++++++++++++++++++++- kernel/rcutiny.c | 16 ++++++++++++---- kernel/rcutree.c | 21 ++++++++++++++------- 3 files changed, 46 insertions(+), 12 deletions(-) (limited to 'kernel') diff --git a/kernel/rcu.h b/kernel/rcu.h index 30876f4063b6..8ba99cdc6515 100644 --- a/kernel/rcu.h +++ b/kernel/rcu.h @@ -33,8 +33,27 @@ * Process-level increment to ->dynticks_nesting field. This allows for * architectures that use half-interrupts and half-exceptions from * process context. + * + * DYNTICK_TASK_NEST_MASK defines a field of width DYNTICK_TASK_NEST_WIDTH + * that counts the number of process-based reasons why RCU cannot + * consider the corresponding CPU to be idle, and DYNTICK_TASK_NEST_VALUE + * is the value used to increment or decrement this field. + * + * The rest of the bits could in principle be used to count interrupts, + * but this would mean that a negative-one value in the interrupt + * field could incorrectly zero out the DYNTICK_TASK_NEST_MASK field. + * We therefore provide a two-bit guard field defined by DYNTICK_TASK_MASK + * that is set to DYNTICK_TASK_FLAG upon initial exit from idle. + * The DYNTICK_TASK_EXIT_IDLE value is thus the combined value used upon + * initial exit from idle. */ -#define DYNTICK_TASK_NESTING (LLONG_MAX / 2 - 1) +#define DYNTICK_TASK_NEST_WIDTH 7 +#define DYNTICK_TASK_NEST_VALUE ((LLONG_MAX >> DYNTICK_TASK_NEST_WIDTH) + 1) +#define DYNTICK_TASK_NEST_MASK (LLONG_MAX - DYNTICK_TASK_NEST_VALUE + 1) +#define DYNTICK_TASK_FLAG ((DYNTICK_TASK_NEST_VALUE / 8) * 2) +#define DYNTICK_TASK_MASK ((DYNTICK_TASK_NEST_VALUE / 8) * 3) +#define DYNTICK_TASK_EXIT_IDLE (DYNTICK_TASK_NEST_VALUE + \ + DYNTICK_TASK_FLAG) /* * debug_rcu_head_queue()/debug_rcu_head_unqueue() are used internally diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c index 4eb34fcc2a75..c8b0e1582c04 100644 --- a/kernel/rcutiny.c +++ b/kernel/rcutiny.c @@ -53,7 +53,7 @@ static void __call_rcu(struct rcu_head *head, #include "rcutiny_plugin.h" -static long long rcu_dynticks_nesting = DYNTICK_TASK_NESTING; +static long long rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; /* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */ static void rcu_idle_enter_common(long long oldval) @@ -88,7 +88,12 @@ void rcu_idle_enter(void) local_irq_save(flags); oldval = rcu_dynticks_nesting; - rcu_dynticks_nesting = 0; + WARN_ON_ONCE((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0); + if ((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == + DYNTICK_TASK_NEST_VALUE) + rcu_dynticks_nesting = 0; + else + rcu_dynticks_nesting -= DYNTICK_TASK_NEST_VALUE; rcu_idle_enter_common(oldval); local_irq_restore(flags); } @@ -140,8 +145,11 @@ void rcu_idle_exit(void) local_irq_save(flags); oldval = rcu_dynticks_nesting; - WARN_ON_ONCE(oldval != 0); - rcu_dynticks_nesting = DYNTICK_TASK_NESTING; + WARN_ON_ONCE(rcu_dynticks_nesting < 0); + if (rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) + rcu_dynticks_nesting += DYNTICK_TASK_NEST_VALUE; + else + rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; rcu_idle_exit_common(oldval); local_irq_restore(flags); } diff --git a/kernel/rcutree.c b/kernel/rcutree.c index df0e3c1bb68e..92b47760edf3 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -198,7 +198,7 @@ void rcu_note_context_switch(int cpu) EXPORT_SYMBOL_GPL(rcu_note_context_switch); DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = { - .dynticks_nesting = DYNTICK_TASK_NESTING, + .dynticks_nesting = DYNTICK_TASK_EXIT_IDLE, .dynticks = ATOMIC_INIT(1), }; @@ -394,7 +394,11 @@ void rcu_idle_enter(void) local_irq_save(flags); rdtp = &__get_cpu_var(rcu_dynticks); oldval = rdtp->dynticks_nesting; - rdtp->dynticks_nesting = 0; + WARN_ON_ONCE((oldval & DYNTICK_TASK_NEST_MASK) == 0); + if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE) + rdtp->dynticks_nesting = 0; + else + rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE; rcu_idle_enter_common(rdtp, oldval); local_irq_restore(flags); } @@ -467,7 +471,7 @@ static void rcu_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval) * Exit idle mode, in other words, -enter- the mode in which RCU * read-side critical sections can occur. * - * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NESTING to + * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to * allow for the possibility of usermode upcalls messing up our count * of interrupt nesting level during the busy period that is just * now starting. @@ -481,8 +485,11 @@ void rcu_idle_exit(void) local_irq_save(flags); rdtp = &__get_cpu_var(rcu_dynticks); oldval = rdtp->dynticks_nesting; - WARN_ON_ONCE(oldval != 0); - rdtp->dynticks_nesting = DYNTICK_TASK_NESTING; + WARN_ON_ONCE(oldval < 0); + if (oldval & DYNTICK_TASK_NEST_MASK) + rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE; + else + rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; rcu_idle_exit_common(rdtp, oldval); local_irq_restore(flags); } @@ -2253,7 +2260,7 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp) rdp->qlen_lazy = 0; rdp->qlen = 0; rdp->dynticks = &per_cpu(rcu_dynticks, cpu); - WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_NESTING); + WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE); WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1); rdp->cpu = cpu; rdp->rsp = rsp; @@ -2281,7 +2288,7 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible) rdp->qlen_last_fqs_check = 0; rdp->n_force_qs_snap = rsp->n_force_qs; rdp->blimit = blimit; - rdp->dynticks->dynticks_nesting = DYNTICK_TASK_NESTING; + rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; atomic_set(&rdp->dynticks->dynticks, (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1); rcu_prepare_for_idle_init(cpu); -- cgit v1.2.3 From 8a2ecf474d3ee8dd5d001490349e422cec52f39f Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 2 Feb 2012 15:42:04 -0800 Subject: rcu: Add RCU_NONIDLE() for idle-loop RCU read-side critical sections RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden in the inner idle loop, that is, between the rcu_idle_enter() and the rcu_idle_exit() -- RCU will happily ignore any such read-side critical sections. However, things like powertop need tracepoints in the inner idle loop. This commit therefore provides an RCU_NONIDLE() macro that can be used to wrap code in the idle loop that requires RCU read-side critical sections. Suggested-by: Steven Rostedt Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett Acked-by: Deepthi Dharwar --- include/linux/rcupdate.h | 27 +++++++++++++++++++++++++++ kernel/rcutiny.c | 2 ++ kernel/rcutree.c | 2 ++ 3 files changed, 31 insertions(+) (limited to 'kernel') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 6ee663c8745a..937217425c47 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -190,6 +190,33 @@ extern void rcu_idle_exit(void); extern void rcu_irq_enter(void); extern void rcu_irq_exit(void); +/** + * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers + * @a: Code that RCU needs to pay attention to. + * + * RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden + * in the inner idle loop, that is, between the rcu_idle_enter() and + * the rcu_idle_exit() -- RCU will happily ignore any such read-side + * critical sections. However, things like powertop need tracepoints + * in the inner idle loop. + * + * This macro provides the way out: RCU_NONIDLE(do_something_with_RCU()) + * will tell RCU that it needs to pay attending, invoke its argument + * (in this example, a call to the do_something_with_RCU() function), + * and then tell RCU to go back to ignoring this CPU. It is permissible + * to nest RCU_NONIDLE() wrappers, but the nesting level is currently + * quite limited. If deeper nesting is required, it will be necessary + * to adjust DYNTICK_TASK_NESTING_VALUE accordingly. + * + * This macro may be used from process-level code only. + */ +#define RCU_NONIDLE(a) \ + do { \ + rcu_idle_exit(); \ + do { a; } while (0); \ + rcu_idle_enter(); \ + } while (0) + /* * Infrastructure to implement the synchronize_() primitives in * TREE_RCU and rcu_barrier_() primitives in TINY_RCU. diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c index c8b0e1582c04..37a5444204d2 100644 --- a/kernel/rcutiny.c +++ b/kernel/rcutiny.c @@ -97,6 +97,7 @@ void rcu_idle_enter(void) rcu_idle_enter_common(oldval); local_irq_restore(flags); } +EXPORT_SYMBOL_GPL(rcu_idle_enter); /* * Exit an interrupt handler towards idle. @@ -153,6 +154,7 @@ void rcu_idle_exit(void) rcu_idle_exit_common(oldval); local_irq_restore(flags); } +EXPORT_SYMBOL_GPL(rcu_idle_exit); /* * Enter an interrupt handler, moving away from idle. diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 92b47760edf3..eacc10b03531 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -402,6 +402,7 @@ void rcu_idle_enter(void) rcu_idle_enter_common(rdtp, oldval); local_irq_restore(flags); } +EXPORT_SYMBOL_GPL(rcu_idle_enter); /** * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle @@ -493,6 +494,7 @@ void rcu_idle_exit(void) rcu_idle_exit_common(rdtp, oldval); local_irq_restore(flags); } +EXPORT_SYMBOL_GPL(rcu_idle_exit); /** * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle -- cgit v1.2.3 From c3ce910b1456a45fa88959af3735bd6b285e54af Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 14 Feb 2012 10:12:54 -0800 Subject: rcu: Eliminate softirq-mediated RCU_FAST_NO_HZ idle-entry loop If a softirq is pending, the current CPU has RCU callbacks pending, and RCU does not immediately need anything from this CPU, then the current code resets the RCU_FAST_NO_HZ state machine. This means that upon exit from the subsequent softirq handler, RCU_FAST_NO_HZ will try really hard to force RCU into dyntick-idle mode. And if the same conditions hold after a few tries (determined by RCU_IDLE_OPT_FLUSHES), the same situation can repeat, possibly endlessly. This scenario is not particularly good for battery lifetime. This commit therefore suppresses the early exit from the RCU_FAST_NO_HZ state machine in the case where there is a softirq pending. This change forces the state machine to retain its memory, and to enter holdoff if this condition persists. Reported-by: "Abou Gazala, Neven M" Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree_plugin.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'kernel') diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index f7ceadf4986e..392a65136a72 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -2133,7 +2133,8 @@ static void rcu_prepare_for_idle(int cpu) /* First time through, initialize the counter. */ per_cpu(rcu_dyntick_drain, cpu) = RCU_IDLE_FLUSHES; } else if (per_cpu(rcu_dyntick_drain, cpu) <= RCU_IDLE_OPT_FLUSHES && - !rcu_pending(cpu)) { + !rcu_pending(cpu) && + !local_softirq_pending()) { /* Can we go dyntick-idle despite still having callbacks? */ trace_rcu_prep_idle("Dyntick with callbacks"); per_cpu(rcu_dyntick_drain, cpu) = 0; -- cgit v1.2.3 From 696a02cc16b182dd78b1f395ae336f449cc90f11 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 16 Feb 2012 21:59:33 -0800 Subject: rcu: Hold off RCU_FAST_NO_HZ after timer posted This commit handles workloads that transition quickly between idle and non-idle, and where the CPU's callbacks cannot be invoked, but where RCU does not have anything immediate for the CPU to do. Without this patch, the RCU_FAST_NO_HZ code can be invoked repeatedly on each entry to idle. The commit sets the per-CPU rcu_dyntick_holdoff variable to hold off further attempts for a tick. Reported-by: "Abou Gazala, Neven M" Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree_plugin.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel') diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 392a65136a72..c023464816be 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -2138,7 +2138,7 @@ static void rcu_prepare_for_idle(int cpu) /* Can we go dyntick-idle despite still having callbacks? */ trace_rcu_prep_idle("Dyntick with callbacks"); per_cpu(rcu_dyntick_drain, cpu) = 0; - per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1; + per_cpu(rcu_dyntick_holdoff, cpu) = jiffies; if (rcu_cpu_has_nonlazy_callbacks(cpu)) hrtimer_start(&per_cpu(rcu_idle_gp_timer, cpu), rcu_idle_gp_wait, HRTIMER_MODE_REL); -- cgit v1.2.3 From 1cc85961e214773cb7d7f2ccbe3bc644dd466df0 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Fri, 17 Feb 2012 13:20:31 -0800 Subject: rcu: Stop spurious warnings from synchronize_sched_expedited synchronize_sched_expedited() is spamming CONFIG_DEBUG_PREEMPT=y users with an unintended warning from the cpu_is_offline() check: use raw_smp_processor_id() instead of smp_processor_id() there. Because the warning is under a get_online_cpus(), it is not possible for any CPUs to go offline, though it is quite possible that the task might migrate between the raw_smp_processor_id() and the check of cpu_is_offline(). This is not a problem because the task cannot migrate from an offline CPU to an online one or vice versa. The point of the check is to verify that synchronize_sched_expedited() is not called from an offline CPU, for example, from a CPU_DYING notifier, or, more important, from an outgoing CPU making its way from its CPU_DYING notifiers to the idle loop. Signed-off-by: Hugh Dickins Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index eacc10b03531..1050d6d3922c 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -2014,7 +2014,7 @@ void synchronize_sched_expedited(void) /* Note that atomic_inc_return() implies full memory barrier. */ firstsnap = snap = atomic_inc_return(&sync_sched_expedited_started); get_online_cpus(); - WARN_ON_ONCE(cpu_is_offline(smp_processor_id())); + WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id())); /* * Each pass through the following loop attempts to force a -- cgit v1.2.3