From: Valentin Schneider <valentin.schneider@arm.com>
To: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>
Cc: Vincent Guittot <vincent.guittot@linaro.org>,
Mel Gorman <mgorman@suse.de>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
linux-kernel@vger.kernel.org, peterz@infradead.org,
Andi Kleen <andi@firstfloor.org>
Subject: Re: [PATCH 2/6] sched: Simplify migration_cpu_stop()
Date: Wed, 24 Feb 2021 15:34:36 +0000 [thread overview]
Message-ID: <jhjmtvt5vjn.mognet@arm.com> (raw)
In-Reply-To: <20210224131355.430014682@infradead.org>
On 24/02/21 13:24, Peter Zijlstra wrote:
> @@ -1950,31 +1931,20 @@ static int migration_cpu_stop(void *data
> goto out;
>
> if (pending) {
> - p->migration_pending = NULL;
> + if (p->migration_pending == pending)
> + p->migration_pending = NULL;
> complete = true;
> }
>
> - /* migrate_enable() -- we must not race against SCA */
> - if (dest_cpu < 0) {
> - /*
> - * When this was migrate_enable() but we no longer
> - * have a @pending, a concurrent SCA 'fixed' things
> - * and we should be valid again. Nothing to do.
> - */
> - if (!pending) {
> - WARN_ON_ONCE(!cpumask_test_cpu(task_cpu(p), &p->cpus_mask));
> - goto out;
> - }
> -
This is fixed by 5+6, but at this patch I think you can have double
completions - I thought this was an issue, but briefly looking at
completion stuff it might not. In any case, consider:
task_cpu(p) == Y
SCA(p, X);
SCA(p, Y);
SCA(p, Y) will uninstall SCA(p, X)'s pending and complete.
migration/Y kicked by SCA(p, X) will grab arg->pending, which is still
SCA(p, X)'s pending and also complete.
> + if (dest_cpu < 0)
> dest_cpu = cpumask_any_distribute(&p->cpus_mask);
> - }
>
> if (task_on_rq_queued(p))
> rq = __migrate_task(rq, &rf, p, dest_cpu);
> else
> p->wake_cpu = dest_cpu;
>
> - } else if (dest_cpu < 0 || pending) {
> + } else if (pending) {
> /*
> * This happens when we get migrated between migrate_enable()'s
> * preempt_enable() and scheduling the stopper task. At that
next prev parent reply other threads:[~2021-02-24 15:49 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-24 12:24 [PATCH 0/6] sched: Fix affine_move_task() wreckage Peter Zijlstra
2021-02-24 12:24 ` [PATCH 1/6] sched: Fix migration_cpu_stop() requeueing Peter Zijlstra
2021-03-01 10:16 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2021-03-06 11:42 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-02-24 12:24 ` [PATCH 2/6] sched: Simplify migration_cpu_stop() Peter Zijlstra
2021-02-24 15:34 ` Valentin Schneider [this message]
2021-02-25 8:45 ` Peter Zijlstra
2021-02-25 11:10 ` Valentin Schneider
2021-03-01 10:16 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2021-03-06 11:42 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-02-24 12:24 ` [PATCH 3/6] sched: Collate affine_move_task() stoppers Peter Zijlstra
2021-03-01 10:16 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2021-03-06 11:42 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-02-24 12:24 ` [PATCH 4/6] sched: Optimize migration_cpu_stop() Peter Zijlstra
2021-03-01 10:16 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2021-03-06 11:42 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-02-24 12:24 ` [PATCH 5/6] sched: Fix affine_move_task() self-concurrency Peter Zijlstra
2021-03-01 10:16 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2021-03-06 11:42 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-02-24 12:24 ` [PATCH 6/6] sched: Simplify set_affinity_pending refcounts Peter Zijlstra
2021-02-24 15:34 ` Valentin Schneider
2021-02-24 15:34 ` Peter Zijlstra
2021-02-24 17:59 ` Valentin Schneider
2021-02-25 9:27 ` Peter Zijlstra
2021-02-25 11:11 ` Valentin Schneider
2021-03-01 10:16 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2021-03-06 11:42 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
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