From e81baf4cb19a9b428ba477fd0423f81672a58817 Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Tue, 11 Dec 2018 12:12:38 +0100 Subject: srcu: Remove srcu_queue_delayed_work_on() srcu_queue_delayed_work_on() disables preemption (and therefore CPU hotplug in RCU's case) and then checks based on its own accounting if a CPU is online. If the CPU is online it uses queue_delayed_work_on() otherwise it fallbacks to queue_delayed_work(). The problem here is that queue_work() on -RT does not work with disabled preemption. queue_work_on() works also on an offlined CPU. queue_delayed_work_on() has the problem that it is possible to program a timer on an offlined CPU. This timer will fire once the CPU is online again. But until then, the timer remains programmed and nothing will happen. Add a local timer which will fire (as requested per delay) on the local CPU and then enqueue the work on the specific CPU. RCUtorture testing with SRCU-P for 24h showed no problems. Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Paul E. McKenney --- kernel/rcu/srcutree.c | 55 ++++++++++++++++++++++----------------------------- kernel/rcu/tree.c | 4 ---- kernel/rcu/tree.h | 8 -------- 3 files changed, 24 insertions(+), 43 deletions(-) (limited to 'kernel') diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 3600d88d8956..7f041f2435df 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -58,6 +58,7 @@ static bool __read_mostly srcu_init_done; static void srcu_invoke_callbacks(struct work_struct *work); static void srcu_reschedule(struct srcu_struct *ssp, unsigned long delay); static void process_srcu(struct work_struct *work); +static void srcu_delay_timer(struct timer_list *t); /* Wrappers for lock acquisition and release, see raw_spin_lock_rcu_node(). */ #define spin_lock_rcu_node(p) \ @@ -156,7 +157,8 @@ static void init_srcu_struct_nodes(struct srcu_struct *ssp, bool is_static) snp->grphi = cpu; } sdp->cpu = cpu; - INIT_DELAYED_WORK(&sdp->work, srcu_invoke_callbacks); + INIT_WORK(&sdp->work, srcu_invoke_callbacks); + timer_setup(&sdp->delay_work, srcu_delay_timer, 0); sdp->ssp = ssp; sdp->grpmask = 1 << (cpu - sdp->mynode->grplo); if (is_static) @@ -386,13 +388,19 @@ void _cleanup_srcu_struct(struct srcu_struct *ssp, bool quiesced) } else { flush_delayed_work(&ssp->work); } - for_each_possible_cpu(cpu) + for_each_possible_cpu(cpu) { + struct srcu_data *sdp = per_cpu_ptr(ssp->sda, cpu); + if (quiesced) { - if (WARN_ON(delayed_work_pending(&per_cpu_ptr(ssp->sda, cpu)->work))) + if (WARN_ON(timer_pending(&sdp->delay_work))) + return; /* Just leak it! */ + if (WARN_ON(work_pending(&sdp->work))) return; /* Just leak it! */ } else { - flush_delayed_work(&per_cpu_ptr(ssp->sda, cpu)->work); + del_timer_sync(&sdp->delay_work); + flush_work(&sdp->work); } + } if (WARN_ON(rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)) != SRCU_STATE_IDLE) || WARN_ON(srcu_readers_active(ssp))) { pr_info("%s: Active srcu_struct %p state: %d\n", @@ -463,39 +471,23 @@ static void srcu_gp_start(struct srcu_struct *ssp) WARN_ON_ONCE(state != SRCU_STATE_SCAN1); } -/* - * Track online CPUs to guide callback workqueue placement. - */ -DEFINE_PER_CPU(bool, srcu_online); -void srcu_online_cpu(unsigned int cpu) +static void srcu_delay_timer(struct timer_list *t) { - WRITE_ONCE(per_cpu(srcu_online, cpu), true); -} + struct srcu_data *sdp = container_of(t, struct srcu_data, delay_work); -void srcu_offline_cpu(unsigned int cpu) -{ - WRITE_ONCE(per_cpu(srcu_online, cpu), false); + queue_work_on(sdp->cpu, rcu_gp_wq, &sdp->work); } -/* - * Place the workqueue handler on the specified CPU if online, otherwise - * just run it whereever. This is useful for placing workqueue handlers - * that are to invoke the specified CPU's callbacks. - */ -static bool srcu_queue_delayed_work_on(int cpu, struct workqueue_struct *wq, - struct delayed_work *dwork, +static void srcu_queue_delayed_work_on(struct srcu_data *sdp, unsigned long delay) { - bool ret; + if (!delay) { + queue_work_on(sdp->cpu, rcu_gp_wq, &sdp->work); + return; + } - preempt_disable(); - if (READ_ONCE(per_cpu(srcu_online, cpu))) - ret = queue_delayed_work_on(cpu, wq, dwork, delay); - else - ret = queue_delayed_work(wq, dwork, delay); - preempt_enable(); - return ret; + timer_reduce(&sdp->delay_work, jiffies + delay); } /* @@ -504,7 +496,7 @@ static bool srcu_queue_delayed_work_on(int cpu, struct workqueue_struct *wq, */ static void srcu_schedule_cbs_sdp(struct srcu_data *sdp, unsigned long delay) { - srcu_queue_delayed_work_on(sdp->cpu, rcu_gp_wq, &sdp->work, delay); + srcu_queue_delayed_work_on(sdp, delay); } /* @@ -1186,7 +1178,8 @@ static void srcu_invoke_callbacks(struct work_struct *work) struct srcu_data *sdp; struct srcu_struct *ssp; - sdp = container_of(work, struct srcu_data, work.work); + sdp = container_of(work, struct srcu_data, work); + ssp = sdp->ssp; rcu_cblist_init(&ready_cbs); spin_lock_irq_rcu_node(sdp); diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 1c4add096078..127255795859 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3408,8 +3408,6 @@ int rcutree_online_cpu(unsigned int cpu) raw_spin_lock_irqsave_rcu_node(rnp, flags); rnp->ffmask |= rdp->grpmask; raw_spin_unlock_irqrestore_rcu_node(rnp, flags); - if (IS_ENABLED(CONFIG_TREE_SRCU)) - srcu_online_cpu(cpu); if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE) return 0; /* Too early in boot for scheduler work. */ sync_sched_exp_online_cleanup(cpu); @@ -3434,8 +3432,6 @@ int rcutree_offline_cpu(unsigned int cpu) raw_spin_unlock_irqrestore_rcu_node(rnp, flags); rcutree_affinity_setting(cpu, cpu); - if (IS_ENABLED(CONFIG_TREE_SRCU)) - srcu_offline_cpu(cpu); return 0; } diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 149557b7c39c..4bba017c703c 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -458,11 +458,3 @@ static void rcu_bind_gp_kthread(void); static bool rcu_nohz_full_cpu(void); static void rcu_dynticks_task_enter(void); static void rcu_dynticks_task_exit(void); - -#ifdef CONFIG_SRCU -void srcu_online_cpu(unsigned int cpu); -void srcu_offline_cpu(unsigned int cpu); -#else /* #ifdef CONFIG_SRCU */ -void srcu_online_cpu(unsigned int cpu) { } -void srcu_offline_cpu(unsigned int cpu) { } -#endif /* #else #ifdef CONFIG_SRCU */ -- cgit v1.2.3