diff options
author | Paul E. McKenney <paulmck@linux.ibm.com> | 2019-01-25 15:32:01 -0800 |
---|---|---|
committer | Paul E. McKenney <paulmck@linux.ibm.com> | 2019-01-25 15:32:01 -0800 |
commit | 7a968bb26a9b09b6e44c48a8036a73e0bc497dbc (patch) | |
tree | 39a347637e7b8b53355670b9919bd0e6955ecb3f | |
parent | 6ba7d681aca22e53385bdb35b1d7662e61905760 (diff) | |
parent | 13dc7d0c7a2ed438f0ec8e9fb365a1256d87cf87 (diff) | |
download | linux-7a968bb26a9b09b6e44c48a8036a73e0bc497dbc.tar.bz2 |
Merge branches 'consolidate.2019.01.26a' and 'fwd.2019.01.26a' into HEAD
consolidate.2019.01.26a: RCU flavor consolidation cleanups.
fwd.2019.01.26a: RCU grace-period forward-progress fixes.
-rw-r--r-- | Documentation/admin-guide/kernel-parameters.txt | 5 | ||||
-rw-r--r-- | kernel/rcu/tree.c | 102 | ||||
-rw-r--r-- | kernel/rcu/tree.h | 17 | ||||
-rw-r--r-- | kernel/rcu/tree_plugin.h | 68 |
4 files changed, 114 insertions, 78 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index b799bcf67d7b..b0dbb2fa401f 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3721,6 +3721,11 @@ This wake_up() will be accompanied by a WARN_ONCE() splat and an ftrace_dump(). + rcutree.sysrq_rcu= [KNL] + Commandeer a sysrq key to dump out Tree RCU's + rcu_node tree with an eye towards determining + why a new grace period has not yet started. + rcuperf.gp_async= [KNL] Measure performance of asynchronous grace-period primitives such as call_rcu(). diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index e53a586b397b..1c4add096078 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -62,6 +62,7 @@ #include <linux/suspend.h> #include <linux/ftrace.h> #include <linux/tick.h> +#include <linux/sysrq.h> #include "tree.h" #include "rcu.h" @@ -115,6 +116,9 @@ int num_rcu_lvl[] = NUM_RCU_LVL_INIT; int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */ /* panic() on RCU Stall sysctl. */ int sysctl_panic_on_rcu_stall __read_mostly; +/* Commandeer a sysrq key to dump RCU's tree. */ +static bool sysrq_rcu; +module_param(sysrq_rcu, bool, 0444); /* * The rcu_scheduler_active variable is initialized to the value @@ -503,6 +507,14 @@ unsigned long rcu_exp_batches_completed(void) EXPORT_SYMBOL_GPL(rcu_exp_batches_completed); /* + * Return the root node of the rcu_state structure. + */ +static struct rcu_node *rcu_get_root(void) +{ + return &rcu_state.node[0]; +} + +/* * Convert a ->gp_state value to a character string. */ static const char *gp_state_getname(short gs) @@ -519,19 +531,30 @@ void show_rcu_gp_kthreads(void) { int cpu; unsigned long j; + unsigned long ja; + unsigned long jr; + unsigned long jw; struct rcu_data *rdp; struct rcu_node *rnp; - j = jiffies - READ_ONCE(rcu_state.gp_activity); - pr_info("%s: wait state: %s(%d) ->state: %#lx delta ->gp_activity %ld\n", + j = jiffies; + ja = j - READ_ONCE(rcu_state.gp_activity); + jr = j - READ_ONCE(rcu_state.gp_req_activity); + jw = j - READ_ONCE(rcu_state.gp_wake_time); + pr_info("%s: wait state: %s(%d) ->state: %#lx delta ->gp_activity %lu ->gp_req_activity %lu ->gp_wake_time %lu ->gp_wake_seq %ld ->gp_seq %ld ->gp_seq_needed %ld ->gp_flags %#x\n", rcu_state.name, gp_state_getname(rcu_state.gp_state), - rcu_state.gp_state, rcu_state.gp_kthread->state, j); + rcu_state.gp_state, + rcu_state.gp_kthread ? rcu_state.gp_kthread->state : 0x1ffffL, + ja, jr, jw, (long)READ_ONCE(rcu_state.gp_wake_seq), + (long)READ_ONCE(rcu_state.gp_seq), + (long)READ_ONCE(rcu_get_root()->gp_seq_needed), + READ_ONCE(rcu_state.gp_flags)); rcu_for_each_node_breadth_first(rnp) { if (ULONG_CMP_GE(rcu_state.gp_seq, rnp->gp_seq_needed)) continue; - pr_info("\trcu_node %d:%d ->gp_seq %lu ->gp_seq_needed %lu\n", - rnp->grplo, rnp->grphi, rnp->gp_seq, - rnp->gp_seq_needed); + pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld\n", + rnp->grplo, rnp->grphi, (long)rnp->gp_seq, + (long)rnp->gp_seq_needed); if (!rcu_is_leaf_node(rnp)) continue; for_each_leaf_node_possible_cpu(rnp, cpu) { @@ -540,14 +563,35 @@ void show_rcu_gp_kthreads(void) ULONG_CMP_GE(rcu_state.gp_seq, rdp->gp_seq_needed)) continue; - pr_info("\tcpu %d ->gp_seq_needed %lu\n", - cpu, rdp->gp_seq_needed); + pr_info("\tcpu %d ->gp_seq_needed %ld\n", + cpu, (long)rdp->gp_seq_needed); } } /* sched_show_task(rcu_state.gp_kthread); */ } EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads); +/* Dump grace-period-request information due to commandeered sysrq. */ +static void sysrq_show_rcu(int key) +{ + show_rcu_gp_kthreads(); +} + +static struct sysrq_key_op sysrq_rcudump_op = { + .handler = sysrq_show_rcu, + .help_msg = "show-rcu(y)", + .action_msg = "Show RCU tree", + .enable_mask = SYSRQ_ENABLE_DUMP, +}; + +static int __init rcu_sysrq_init(void) +{ + if (sysrq_rcu) + return register_sysrq_key('y', &sysrq_rcudump_op); + return 0; +} +early_initcall(rcu_sysrq_init); + /* * Send along grace-period-related data for rcutorture diagnostics. */ @@ -566,14 +610,6 @@ void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags, EXPORT_SYMBOL_GPL(rcutorture_get_gp_data); /* - * Return the root node of the rcu_state structure. - */ -static struct rcu_node *rcu_get_root(void) -{ - return &rcu_state.node[0]; -} - -/* * Enter an RCU extended quiescent state, which can be either the * idle loop or adaptive-tickless usermode execution. * @@ -1169,7 +1205,7 @@ static void rcu_check_gp_kthread_starvation(void) pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx ->cpu=%d\n", rcu_state.name, j, (long)rcu_seq_current(&rcu_state.gp_seq), - rcu_state.gp_flags, + READ_ONCE(rcu_state.gp_flags), gp_state_getname(rcu_state.gp_state), rcu_state.gp_state, gpk ? gpk->state : ~0, gpk ? task_cpu(gpk) : -1); if (gpk) { @@ -1545,17 +1581,28 @@ static bool rcu_future_gp_cleanup(struct rcu_node *rnp) } /* - * Awaken the grace-period kthread. Don't do a self-awaken, and don't - * bother awakening when there is nothing for the grace-period kthread - * to do (as in several CPUs raced to awaken, and we lost), and finally - * don't try to awaken a kthread that has not yet been created. + * Awaken the grace-period kthread. Don't do a self-awaken (unless in + * an interrupt or softirq handler), and don't bother awakening when there + * is nothing for the grace-period kthread to do (as in several CPUs raced + * to awaken, and we lost), and finally don't try to awaken a kthread that + * has not yet been created. If all those checks are passed, track some + * debug information and awaken. + * + * So why do the self-wakeup when in an interrupt or softirq handler + * in the grace-period kthread's context? Because the kthread might have + * been interrupted just as it was going to sleep, and just after the final + * pre-sleep check of the awaken condition. In this case, a wakeup really + * is required, and is therefore supplied. */ static void rcu_gp_kthread_wake(void) { - if (current == rcu_state.gp_kthread || + if ((current == rcu_state.gp_kthread && + !in_interrupt() && !in_serving_softirq()) || !READ_ONCE(rcu_state.gp_flags) || !rcu_state.gp_kthread) return; + WRITE_ONCE(rcu_state.gp_wake_time, jiffies); + WRITE_ONCE(rcu_state.gp_wake_seq, READ_ONCE(rcu_state.gp_seq)); swake_up_one(&rcu_state.gp_wq); } @@ -1699,7 +1746,7 @@ static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp) zero_cpu_stall_ticks(rdp); } rdp->gp_seq = rnp->gp_seq; /* Remember new grace-period state. */ - if (ULONG_CMP_GE(rnp->gp_seq_needed, rdp->gp_seq_needed) || rdp->gpwrap) + if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap) rdp->gp_seq_needed = rnp->gp_seq_needed; WRITE_ONCE(rdp->gpwrap, false); rcu_gpnum_ovf(rnp, rdp); @@ -1927,7 +1974,7 @@ static void rcu_gp_fqs_loop(void) if (!ret) { rcu_state.jiffies_force_qs = jiffies + j; WRITE_ONCE(rcu_state.jiffies_kick_kthreads, - jiffies + 3 * j); + jiffies + (j ? 3 * j : 2)); } trace_rcu_grace_period(rcu_state.name, READ_ONCE(rcu_state.gp_seq), @@ -2646,16 +2693,11 @@ rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp, raw_spin_unlock_irqrestore_rcu_node(rnp, flags); return; } - pr_alert("%s: g%ld->%ld gar:%lu ga:%lu f%#x gs:%d %s->state:%#lx\n", - __func__, (long)READ_ONCE(rcu_state.gp_seq), - (long)READ_ONCE(rnp_root->gp_seq_needed), - j - rcu_state.gp_req_activity, j - rcu_state.gp_activity, - rcu_state.gp_flags, rcu_state.gp_state, rcu_state.name, - rcu_state.gp_kthread ? rcu_state.gp_kthread->state : 0x1ffffL); WARN_ON(1); if (rnp_root != rnp) raw_spin_unlock_rcu_node(rnp_root); raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + show_rcu_gp_kthreads(); } /* diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 20feecbb0ab6..149557b7c39c 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -230,7 +230,13 @@ struct rcu_data { /* Leader CPU takes GP-end wakeups. */ #endif /* #ifdef CONFIG_RCU_NOCB_CPU */ - /* 6) Diagnostic data, including RCU CPU stall warnings. */ + /* 6) RCU priority boosting. */ + struct task_struct *rcu_cpu_kthread_task; + /* rcuc per-CPU kthread or NULL. */ + unsigned int rcu_cpu_kthread_status; + char rcu_cpu_has_work; + + /* 7) Diagnostic data, including RCU CPU stall warnings. */ unsigned int softirq_snap; /* Snapshot of softirq activity. */ /* ->rcu_iw* fields protected by leaf rcu_node ->lock. */ struct irq_work rcu_iw; /* Check for non-irq activity. */ @@ -299,6 +305,8 @@ struct rcu_state { struct swait_queue_head gp_wq; /* Where GP task waits. */ short gp_flags; /* Commands for GP task. */ short gp_state; /* GP kthread sleep state. */ + unsigned long gp_wake_time; /* Last GP kthread wake. */ + unsigned long gp_wake_seq; /* ->gp_seq at ^^^. */ /* End of fields guarded by root rcu_node's lock. */ @@ -398,13 +406,6 @@ static const char *tp_rcu_varname __used __tracepoint_string = rcu_name; int rcu_dynticks_snap(struct rcu_data *rdp); -#ifdef CONFIG_RCU_BOOST -DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_status); -DECLARE_PER_CPU(int, rcu_cpu_kthread_cpu); -DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_loops); -DECLARE_PER_CPU(char, rcu_cpu_has_work); -#endif /* #ifdef CONFIG_RCU_BOOST */ - /* Forward declarations for rcutree_plugin.h */ static void rcu_bootup_announce(void); static void rcu_qs(void); diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index abd238c70900..8ceed9e25ad5 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -34,17 +34,7 @@ #include "../time/tick-internal.h" #ifdef CONFIG_RCU_BOOST - #include "../locking/rtmutex_common.h" - -/* - * Control variables for per-CPU and per-rcu_node kthreads. - */ -static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task); -DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status); -DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops); -DEFINE_PER_CPU(char, rcu_cpu_has_work); - #else /* #ifdef CONFIG_RCU_BOOST */ /* @@ -1243,11 +1233,11 @@ static void invoke_rcu_callbacks_kthread(void) unsigned long flags; local_irq_save(flags); - __this_cpu_write(rcu_cpu_has_work, 1); - if (__this_cpu_read(rcu_cpu_kthread_task) != NULL && - current != __this_cpu_read(rcu_cpu_kthread_task)) { - rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task), - __this_cpu_read(rcu_cpu_kthread_status)); + __this_cpu_write(rcu_data.rcu_cpu_has_work, 1); + if (__this_cpu_read(rcu_data.rcu_cpu_kthread_task) != NULL && + current != __this_cpu_read(rcu_data.rcu_cpu_kthread_task)) { + rcu_wake_cond(__this_cpu_read(rcu_data.rcu_cpu_kthread_task), + __this_cpu_read(rcu_data.rcu_cpu_kthread_status)); } local_irq_restore(flags); } @@ -1258,7 +1248,7 @@ static void invoke_rcu_callbacks_kthread(void) */ static bool rcu_is_callbacks_kthread(void) { - return __this_cpu_read(rcu_cpu_kthread_task) == current; + return __this_cpu_read(rcu_data.rcu_cpu_kthread_task) == current; } #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) @@ -1315,12 +1305,12 @@ static void rcu_cpu_kthread_setup(unsigned int cpu) static void rcu_cpu_kthread_park(unsigned int cpu) { - per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; + per_cpu(rcu_data.rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; } static int rcu_cpu_kthread_should_run(unsigned int cpu) { - return __this_cpu_read(rcu_cpu_has_work); + return __this_cpu_read(rcu_data.rcu_cpu_has_work); } /* @@ -1330,15 +1320,14 @@ static int rcu_cpu_kthread_should_run(unsigned int cpu) */ static void rcu_cpu_kthread(unsigned int cpu) { - unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status); - char work, *workp = this_cpu_ptr(&rcu_cpu_has_work); + unsigned int *statusp = this_cpu_ptr(&rcu_data.rcu_cpu_kthread_status); + char work, *workp = this_cpu_ptr(&rcu_data.rcu_cpu_has_work); int spincnt; for (spincnt = 0; spincnt < 10; spincnt++) { trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait")); local_bh_disable(); *statusp = RCU_KTHREAD_RUNNING; - this_cpu_inc(rcu_cpu_kthread_loops); local_irq_disable(); work = *workp; *workp = 0; @@ -1390,7 +1379,7 @@ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) } static struct smp_hotplug_thread rcu_cpu_thread_spec = { - .store = &rcu_cpu_kthread_task, + .store = &rcu_data.rcu_cpu_kthread_task, .thread_should_run = rcu_cpu_kthread_should_run, .thread_fn = rcu_cpu_kthread, .thread_comm = "rcuc/%u", @@ -1407,7 +1396,7 @@ static void __init rcu_spawn_boost_kthreads(void) int cpu; for_each_possible_cpu(cpu) - per_cpu(rcu_cpu_has_work, cpu) = 0; + per_cpu(rcu_data.rcu_cpu_has_work, cpu) = 0; if (WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec), "%s: Could not start rcub kthread, OOM is now expected behavior\n", __func__)) return; rcu_for_each_leaf_node(rnp) @@ -1773,22 +1762,24 @@ static void zero_cpu_stall_ticks(struct rcu_data *rdp) /* * Offload callback processing from the boot-time-specified set of CPUs - * specified by rcu_nocb_mask. For each CPU in the set, there is a - * kthread created that pulls the callbacks from the corresponding CPU, - * waits for a grace period to elapse, and invokes the callbacks. - * The no-CBs CPUs do a wake_up() on their kthread when they insert - * a callback into any empty list, unless the rcu_nocb_poll boot parameter - * has been specified, in which case each kthread actively polls its - * CPU. (Which isn't so great for energy efficiency, but which does - * reduce RCU's overhead on that CPU.) + * specified by rcu_nocb_mask. For the CPUs in the set, there are kthreads + * created that pull the callbacks from the corresponding CPU, wait for + * a grace period to elapse, and invoke the callbacks. These kthreads + * are organized into leaders, which manage incoming callbacks, wait for + * grace periods, and awaken followers, and the followers, which only + * invoke callbacks. Each leader is its own follower. The no-CBs CPUs + * do a wake_up() on their kthread when they insert a callback into any + * empty list, unless the rcu_nocb_poll boot parameter has been specified, + * in which case each kthread actively polls its CPU. (Which isn't so great + * for energy efficiency, but which does reduce RCU's overhead on that CPU.) * * This is intended to be used in conjunction with Frederic Weisbecker's * adaptive-idle work, which would seriously reduce OS jitter on CPUs * running CPU-bound user-mode computations. * - * Offloading of callback processing could also in theory be used as - * an energy-efficiency measure because CPUs with no RCU callbacks - * queued are more aggressive about entering dyntick-idle mode. + * Offloading of callbacks can also be used as an energy-efficiency + * measure because CPUs with no RCU callbacks queued are more aggressive + * about entering dyntick-idle mode. */ @@ -1892,10 +1883,7 @@ static void wake_nocb_leader_defer(struct rcu_data *rdp, int waketype, raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags); } -/* - * Does the specified CPU need an RCU callback for this invocation - * of rcu_barrier()? - */ +/* Does rcu_barrier need to queue an RCU callback on the specified CPU? */ static bool rcu_nocb_cpu_needs_barrier(int cpu) { struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); @@ -1911,8 +1899,8 @@ static bool rcu_nocb_cpu_needs_barrier(int cpu) * callbacks would be posted. In the worst case, the first * barrier in rcu_barrier() suffices (but the caller cannot * necessarily rely on this, not a substitute for the caller - * getting the concurrency design right!). There must also be - * a barrier between the following load an posting of a callback + * getting the concurrency design right!). There must also be a + * barrier between the following load and posting of a callback * (if a callback is in fact needed). This is associated with an * atomic_inc() in the caller. */ |