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;
next prev parent reply other threads:[~2020-11-17 12:52 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-16 9:10 Loadavg accounting error on arm64 Mel Gorman
2020-11-16 11:49 ` Mel Gorman
2020-11-16 12:00 ` Mel Gorman
2020-11-16 12:53 ` Peter Zijlstra
2020-11-16 12:58 ` Peter Zijlstra
2020-11-16 15:29 ` Mel Gorman
2020-11-16 16:42 ` Mel Gorman
2020-11-16 16:49 ` Peter Zijlstra
2020-11-16 17:24 ` Mel Gorman
2020-11-16 17:41 ` Will Deacon
2020-11-16 12:46 ` Peter Zijlstra
2020-11-16 12:58 ` Mel Gorman
2020-11-16 13:11 ` Will Deacon
2020-11-16 13:37 ` Mel Gorman
2020-11-16 14:20 ` Peter Zijlstra
2020-11-16 15:52 ` Mel Gorman
2020-11-16 16:54 ` Peter Zijlstra
2020-11-16 17:16 ` 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 9:15 ` Will Deacon
2020-11-17 9:29 ` Peter Zijlstra
2020-11-17 9:46 ` Peter Zijlstra
2020-11-17 10:36 ` Will Deacon
2020-11-17 12:52 ` Valentin Schneider [this message]
2020-11-17 15:37 ` Valentin Schneider
2020-11-17 16:13 ` Peter Zijlstra
2020-11-17 19:32 ` Valentin Schneider
2020-11-18 8:05 ` Peter Zijlstra
2020-11-18 9:51 ` Valentin Schneider
2020-11-18 13:33 ` Marco Elver
2020-11-17 9:38 ` [PATCH] sched: Fix rq->nr_iowait ordering Peter Zijlstra
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
2020-11-19 9:55 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
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