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Date: Fri, 24 Apr 2020 10:52:38 -0700 From: Suren Baghdasaryan <surenb@...gle.com> To: Peter Zijlstra <peterz@...radead.org> Cc: Ingo Molnar <mingo@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>, will@...nel.org, Johannes Weiner <hannes@...xchg.org>, Shakeel Butt <shakeelb@...gle.com>, LKML <linux-kernel@...r.kernel.org>, kernel-team <kernel-team@...roid.com> Subject: Re: lockdep warning about possible circular dependency in PSI On Fri, Apr 24, 2020 at 10:40 AM Peter Zijlstra <peterz@...radead.org> wrote: > > On Fri, Apr 24, 2020 at 09:34:42AM -0700, Suren Baghdasaryan wrote: > > Sorry to bother you again folks. Any suggestions on how to silence > > this lockdep warning which I believe to be a false positive? > > > > On Wed, Apr 15, 2020 at 4:01 PM Suren Baghdasaryan <surenb@...gle.com> wrote: > > > > > > I received a report about possible circular locking dependency warning > > > generated from PSI polling code. I think we are protected from this > > > scenario by poll_scheduled atomic but wanted to double-check and I’m > > > looking for an advice on how to annotate this case to fix the lockdep > > > warning. I copied the detailed information at the end of this email > > > but the short story is this: > > > > > > "WARNING: possible circular locking dependency detected" is generated > > > with CONFIG_PSI and CONFIG_LOCKDEP enabled. The dependency chain it > > > describes is: > > > > > > #0 > > > kthread_delayed_work_timer_fn() > > > | > > > worker->lock > > > | > > > try_to_wake_up() > > > | > > > p->pi_lock > > > > > > #1 > > > sched_fork() > > > | > > > p->pi_lock > > > | > > > task_fork_fair() > > > | > > > rq->lock > > > > > > #2 > > > psi_memstall_enter > > > | > > > rq->lock > > > | > > > kthread_queue_delayed_work() > > > | > > > worker->lock > > Irrespective of it actually being a deadlock or not, it is fairly > fragile. Ideally we'd fix #2, we really should minimize the number of > locks nested under rq->lock. > > That said, here's the easy fix, which breaks #0. > Thanks for the suggestion, Peter. Let me digest this and will post a patch with your Suggested-by. Cheers! > --- > diff --git a/kernel/kthread.c b/kernel/kthread.c > index bfbfa481be3a..b443bba7dd21 100644 > --- a/kernel/kthread.c > +++ b/kernel/kthread.c > @@ -806,14 +806,15 @@ static void kthread_insert_work_sanity_check(struct kthread_worker *worker, > /* insert @work before @pos in @worker */ > static void kthread_insert_work(struct kthread_worker *worker, > struct kthread_work *work, > - struct list_head *pos) > + struct list_head *pos, > + struct wake_q_head *wake_q) > { > kthread_insert_work_sanity_check(worker, work); > > list_add_tail(&work->node, pos); > work->worker = worker; > if (!worker->current_work && likely(worker->task)) > - wake_up_process(worker->task); > + wake_q_add(wake_q, worker->task); > } > > /** > @@ -831,15 +832,19 @@ static void kthread_insert_work(struct kthread_worker *worker, > bool kthread_queue_work(struct kthread_worker *worker, > struct kthread_work *work) > { > - bool ret = false; > + DEFINE_WAKE_Q(wake_q); > unsigned long flags; > + bool ret = false; > > raw_spin_lock_irqsave(&worker->lock, flags); > if (!queuing_blocked(worker, work)) { > - kthread_insert_work(worker, work, &worker->work_list); > + kthread_insert_work(worker, work, &worker->work_list, &wake_q); > ret = true; > } > raw_spin_unlock_irqrestore(&worker->lock, flags); > + > + wake_up_q(&wake_q); > + > return ret; > } > EXPORT_SYMBOL_GPL(kthread_queue_work); > @@ -857,6 +862,7 @@ void kthread_delayed_work_timer_fn(struct timer_list *t) > struct kthread_delayed_work *dwork = from_timer(dwork, t, timer); > struct kthread_work *work = &dwork->work; > struct kthread_worker *worker = work->worker; > + DEFINE_WAKE_Q(wake_q); > unsigned long flags; > > /* > @@ -873,15 +879,18 @@ void kthread_delayed_work_timer_fn(struct timer_list *t) > /* Move the work from worker->delayed_work_list. */ > WARN_ON_ONCE(list_empty(&work->node)); > list_del_init(&work->node); > - kthread_insert_work(worker, work, &worker->work_list); > + kthread_insert_work(worker, work, &worker->work_list, &wake_q); > > raw_spin_unlock_irqrestore(&worker->lock, flags); > + > + wake_up_q(&wake_q); > } > EXPORT_SYMBOL(kthread_delayed_work_timer_fn); > > static void __kthread_queue_delayed_work(struct kthread_worker *worker, > struct kthread_delayed_work *dwork, > - unsigned long delay) > + unsigned long delay, > + struct wake_q_head *wake_q) > { > struct timer_list *timer = &dwork->timer; > struct kthread_work *work = &dwork->work; > @@ -895,7 +904,7 @@ static void __kthread_queue_delayed_work(struct kthread_worker *worker, > * on that there's no such delay when @delay is 0. > */ > if (!delay) { > - kthread_insert_work(worker, work, &worker->work_list); > + kthread_insert_work(worker, work, &worker->work_list, wake_q); > return; > } > > @@ -928,17 +937,21 @@ bool kthread_queue_delayed_work(struct kthread_worker *worker, > unsigned long delay) > { > struct kthread_work *work = &dwork->work; > + DEFINE_WAKE_Q(wake_q); > unsigned long flags; > bool ret = false; > > raw_spin_lock_irqsave(&worker->lock, flags); > > if (!queuing_blocked(worker, work)) { > - __kthread_queue_delayed_work(worker, dwork, delay); > + __kthread_queue_delayed_work(worker, dwork, delay, &wake_q); > ret = true; > } > > raw_spin_unlock_irqrestore(&worker->lock, flags); > + > + wake_up_q(&wake_q); > + > return ret; > } > EXPORT_SYMBOL_GPL(kthread_queue_delayed_work); > @@ -967,6 +980,7 @@ void kthread_flush_work(struct kthread_work *work) > KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn), > COMPLETION_INITIALIZER_ONSTACK(fwork.done), > }; > + DEFINE_WAKE_Q(wake_q); > struct kthread_worker *worker; > bool noop = false; > > @@ -979,15 +993,17 @@ void kthread_flush_work(struct kthread_work *work) > WARN_ON_ONCE(work->worker != worker); > > if (!list_empty(&work->node)) > - kthread_insert_work(worker, &fwork.work, work->node.next); > + kthread_insert_work(worker, &fwork.work, work->node.next, &wake_q); > else if (worker->current_work == work) > kthread_insert_work(worker, &fwork.work, > - worker->work_list.next); > + worker->work_list.next, &wake_q); > else > noop = true; > > raw_spin_unlock_irq(&worker->lock); > > + wake_up_q(&wake_q); > + > if (!noop) > wait_for_completion(&fwork.done); > } > @@ -1065,6 +1081,7 @@ bool kthread_mod_delayed_work(struct kthread_worker *worker, > unsigned long delay) > { > struct kthread_work *work = &dwork->work; > + DEFINE_WAKE_Q(wake_q); > unsigned long flags; > int ret = false; > > @@ -1083,9 +1100,12 @@ bool kthread_mod_delayed_work(struct kthread_worker *worker, > > ret = __kthread_cancel_work(work, true, &flags); > fast_queue: > - __kthread_queue_delayed_work(worker, dwork, delay); > + __kthread_queue_delayed_work(worker, dwork, delay, &wake_q); > out: > raw_spin_unlock_irqrestore(&worker->lock, flags); > + > + wake_up_q(&wake_q); > + > return ret; > } > EXPORT_SYMBOL_GPL(kthread_mod_delayed_work); > > -- > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@...roid.com. >
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