From: Valentin Schneider <valentin.schneider@arm.com> To: Peter Zijlstra <peterz@infradead.org> Cc: Will Deacon <will@kernel.org>, Mel Gorman <mgorman@techsingularity.net>, Davidlohr Bueso <dave@stgolabs.net>, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] sched: Fix data-race in wakeup Date: Tue, 17 Nov 2020 12:52:12 +0000 [thread overview] Message-ID: <jhjv9e4w3gj.mognet@arm.com> (raw) In-Reply-To: <20201117094621.GE3121429@hirez.programming.kicks-ass.net> On 17/11/20 09:46, Peter Zijlstra wrote: > How's this then? It still doesn't explicitly call out the specific race, > but does mention the more fundamental issue that wakelist queueing > doesn't respect the regular rules anymore. > > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -775,7 +775,6 @@ struct task_struct { > unsigned sched_reset_on_fork:1; > unsigned sched_contributes_to_load:1; > unsigned sched_migrated:1; > - unsigned sched_remote_wakeup:1; > #ifdef CONFIG_PSI > unsigned sched_psi_wake_requeue:1; > #endif > @@ -785,6 +784,21 @@ struct task_struct { > > /* Unserialized, strictly 'current' */ > > + /* > + * This field must not be in the scheduler word above due to wakelist > + * queueing no longer being serialized by p->on_cpu. However: > + * > + * p->XXX = X; ttwu() > + * schedule() if (p->on_rq && ..) // false > + * smp_mb__after_spinlock(); if (smp_load_acquire(&p->on_cpu) && //true > + * deactivate_task() ttwu_queue_wakelist()) > + * p->on_rq = 0; p->sched_remote_wakeup = Y; > + * > + * guarantees all stores of 'current' are visible before > + * ->sched_remote_wakeup gets used, so it can be in this word. > + */ Isn't the control dep between that ttwu() p->on_rq read and p->sched_remote_wakeup write "sufficient"? That should be giving the right ordering for the rest of ttwu() wrt. those 'current' bits, considering they are written before that smp_mb__after_spinlock(). In any case, consider me convinced: Reviewed-by: Valentin Schneider <valentin.schneider@arm.com> > + unsigned sched_remote_wakeup:1; > + > /* Bit to tell LSMs we're in execve(): */ > unsigned in_execve:1; > unsigned in_iowait:1;
WARNING: multiple messages have this Message-ID (diff)
From: Valentin Schneider <valentin.schneider@arm.com> To: Peter Zijlstra <peterz@infradead.org> Cc: Mel Gorman <mgorman@techsingularity.net>, Davidlohr Bueso <dave@stgolabs.net>, Will Deacon <will@kernel.org>, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] sched: Fix data-race in wakeup Date: Tue, 17 Nov 2020 12:52:12 +0000 [thread overview] Message-ID: <jhjv9e4w3gj.mognet@arm.com> (raw) In-Reply-To: <20201117094621.GE3121429@hirez.programming.kicks-ass.net> On 17/11/20 09:46, Peter Zijlstra wrote: > How's this then? It still doesn't explicitly call out the specific race, > but does mention the more fundamental issue that wakelist queueing > doesn't respect the regular rules anymore. > > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -775,7 +775,6 @@ struct task_struct { > unsigned sched_reset_on_fork:1; > unsigned sched_contributes_to_load:1; > unsigned sched_migrated:1; > - unsigned sched_remote_wakeup:1; > #ifdef CONFIG_PSI > unsigned sched_psi_wake_requeue:1; > #endif > @@ -785,6 +784,21 @@ struct task_struct { > > /* Unserialized, strictly 'current' */ > > + /* > + * This field must not be in the scheduler word above due to wakelist > + * queueing no longer being serialized by p->on_cpu. However: > + * > + * p->XXX = X; ttwu() > + * schedule() if (p->on_rq && ..) // false > + * smp_mb__after_spinlock(); if (smp_load_acquire(&p->on_cpu) && //true > + * deactivate_task() ttwu_queue_wakelist()) > + * p->on_rq = 0; p->sched_remote_wakeup = Y; > + * > + * guarantees all stores of 'current' are visible before > + * ->sched_remote_wakeup gets used, so it can be in this word. > + */ Isn't the control dep between that ttwu() p->on_rq read and p->sched_remote_wakeup write "sufficient"? That should be giving the right ordering for the rest of ttwu() wrt. those 'current' bits, considering they are written before that smp_mb__after_spinlock(). In any case, consider me convinced: Reviewed-by: Valentin Schneider <valentin.schneider@arm.com> > + unsigned sched_remote_wakeup:1; > + > /* Bit to tell LSMs we're in execve(): */ > unsigned in_execve:1; > unsigned in_iowait:1; _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-11-17 12:52 UTC|newest] Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-11-16 9:10 Loadavg accounting error on arm64 Mel Gorman 2020-11-16 9:10 ` Mel Gorman 2020-11-16 11:49 ` Mel Gorman 2020-11-16 11:49 ` Mel Gorman 2020-11-16 12:00 ` Mel Gorman 2020-11-16 12:00 ` Mel Gorman 2020-11-16 12:53 ` Peter Zijlstra 2020-11-16 12:53 ` Peter Zijlstra 2020-11-16 12:58 ` Peter Zijlstra 2020-11-16 12:58 ` Peter Zijlstra 2020-11-16 15:29 ` Mel Gorman 2020-11-16 15:29 ` Mel Gorman 2020-11-16 16:42 ` Mel Gorman 2020-11-16 16:42 ` Mel Gorman 2020-11-16 16:49 ` Peter Zijlstra 2020-11-16 16:49 ` Peter Zijlstra 2020-11-16 17:24 ` Mel Gorman 2020-11-16 17:24 ` Mel Gorman 2020-11-16 17:41 ` Will Deacon 2020-11-16 17:41 ` Will Deacon 2020-11-16 12:46 ` Peter Zijlstra 2020-11-16 12:46 ` Peter Zijlstra 2020-11-16 12:58 ` Mel Gorman 2020-11-16 12:58 ` Mel Gorman 2020-11-16 13:11 ` Will Deacon 2020-11-16 13:11 ` Will Deacon 2020-11-16 13:37 ` Mel Gorman 2020-11-16 13:37 ` Mel Gorman 2020-11-16 14:20 ` Peter Zijlstra 2020-11-16 14:20 ` Peter Zijlstra 2020-11-16 15:52 ` Mel Gorman 2020-11-16 15:52 ` Mel Gorman 2020-11-16 16:54 ` Peter Zijlstra 2020-11-16 16:54 ` Peter Zijlstra 2020-11-16 17:16 ` Mel Gorman 2020-11-16 17:16 ` Mel Gorman 2020-11-16 19:31 ` Mel Gorman 2020-11-16 19:31 ` Mel Gorman 2020-11-17 8:30 ` [PATCH] sched: Fix data-race in wakeup Peter Zijlstra 2020-11-17 8:30 ` Peter Zijlstra 2020-11-17 9:15 ` Will Deacon 2020-11-17 9:15 ` Will Deacon 2020-11-17 9:29 ` Peter Zijlstra 2020-11-17 9:29 ` Peter Zijlstra 2020-11-17 9:46 ` Peter Zijlstra 2020-11-17 9:46 ` Peter Zijlstra 2020-11-17 10:36 ` Will Deacon 2020-11-17 10:36 ` Will Deacon 2020-11-17 12:52 ` Valentin Schneider [this message] 2020-11-17 12:52 ` Valentin Schneider 2020-11-17 15:37 ` Valentin Schneider 2020-11-17 15:37 ` Valentin Schneider 2020-11-17 16:13 ` Peter Zijlstra 2020-11-17 16:13 ` Peter Zijlstra 2020-11-17 19:32 ` Valentin Schneider 2020-11-17 19:32 ` Valentin Schneider 2020-11-18 8:05 ` Peter Zijlstra 2020-11-18 8:05 ` Peter Zijlstra 2020-11-18 9:51 ` Valentin Schneider 2020-11-18 9:51 ` Valentin Schneider 2020-11-18 13:33 ` Marco Elver 2020-11-18 13:33 ` Marco Elver 2020-11-17 9:38 ` [PATCH] sched: Fix rq->nr_iowait ordering Peter Zijlstra 2020-11-17 9:38 ` Peter Zijlstra 2020-11-17 11:43 ` Mel Gorman 2020-11-17 11:43 ` Mel Gorman 2020-11-19 9:55 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra 2020-11-17 12:40 ` [PATCH] sched: Fix data-race in wakeup Mel Gorman 2020-11-17 12:40 ` Mel Gorman 2020-11-19 9:55 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
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