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From: Peter Zijlstra <peterz@infradead.org>
To: Valentin Schneider <valentin.schneider@arm.com>
Cc: tglx@linutronix.de, mingo@kernel.org,
	linux-kernel@vger.kernel.org, bigeasy@linutronix.de,
	qais.yousef@arm.com, swood@redhat.com, juri.lelli@redhat.com,
	vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
	rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
	bristot@redhat.com, vincent.donnefort@arm.com
Subject: Re: [PATCH 8/9] sched: Fix migrate_disable() vs set_cpus_allowed_ptr()
Date: Fri, 25 Sep 2020 10:43:39 +0200	[thread overview]
Message-ID: <20200925084339.GU2628@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <jhj3637lzdm.mognet@arm.com>

On Thu, Sep 24, 2020 at 08:59:33PM +0100, Valentin Schneider wrote:

> > +	if (task_running(rq, p) || p->state == TASK_WAKING) {
> > +
> > +		task_rq_unlock(rq, p, rf);
> > +		stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg);
> > +
> 
> Shouldn't we check for is_migrate_disabled(p) before doing any of that?
> migration_cpu_stop() does check for it, is there something that prevents us
> from acting on it earlier than that?

Since migrate_disable() / ->migration_disabled is only touched from the
current task, you can only reliably read it from the same CPU.

Hence I only look at it when the stop task has pinned the task, because
at that point I know it's stable.

Doing it earlier gives races, races give me head-aches. This is a slow
path, I don't care about performance.

  reply	other threads:[~2020-09-25  8:44 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-21 16:35 [PATCH 0/9] sched: Migrate disable support Peter Zijlstra
2020-09-21 16:35 ` [PATCH 1/9] stop_machine: Add function and caller debug info Peter Zijlstra
2020-09-21 16:35 ` [PATCH 2/9] sched: Fix balance_callback() Peter Zijlstra
2020-09-23 14:08   ` Thomas Gleixner
2020-09-21 16:36 ` [PATCH 3/9] sched/hotplug: Ensure only per-cpu kthreads run during hotplug Peter Zijlstra
2020-09-25 16:38   ` Dietmar Eggemann
2020-10-02 14:20     ` Peter Zijlstra
2020-09-21 16:36 ` [PATCH 4/9] sched/core: Wait for tasks being pushed away on hotplug Peter Zijlstra
2020-09-21 16:36 ` [PATCH 5/9] sched/hotplug: Consolidate task migration on CPU unplug Peter Zijlstra
2020-10-01 17:12   ` Vincent Donnefort
2020-10-02 14:17     ` Peter Zijlstra
2020-09-21 16:36 ` [PATCH 6/9] sched: Massage set_cpus_allowed Peter Zijlstra
2020-09-23 14:07   ` Thomas Gleixner
2020-09-21 16:36 ` [PATCH 7/9] sched: Add migrate_disable() Peter Zijlstra
2020-09-21 19:16   ` Thomas Gleixner
2020-09-21 20:42     ` Daniel Bristot de Oliveira
2020-09-23  8:31       ` Thomas Gleixner
2020-09-23 10:51         ` Daniel Bristot de Oliveira
2020-09-23 17:08         ` peterz
2020-09-23 17:54           ` Daniel Bristot de Oliveira
2020-09-23  7:48     ` peterz
2020-09-24 11:53   ` Valentin Schneider
2020-09-24 12:29     ` Peter Zijlstra
2020-09-24 12:33       ` Valentin Schneider
2020-09-24 12:35     ` Peter Zijlstra
2020-09-25 16:50   ` Sebastian Andrzej Siewior
2020-10-02 14:21     ` Peter Zijlstra
2020-10-02 14:36       ` Sebastian Andrzej Siewior
2020-09-21 16:36 ` [PATCH 8/9] sched: Fix migrate_disable() vs set_cpus_allowed_ptr() Peter Zijlstra
2020-09-24 19:59   ` Valentin Schneider
2020-09-25  8:43     ` Peter Zijlstra [this message]
2020-09-25 10:07       ` Valentin Schneider
2020-09-25  9:05     ` Peter Zijlstra
2020-09-25  9:56       ` Peter Zijlstra
2020-09-25 10:09         ` Valentin Schneider
2020-09-21 16:36 ` [PATCH 9/9] sched/core: Make migrate disable and CPU hotplug cooperative Peter Zijlstra
2020-09-25  9:12 ` [PATCH 0/9] sched: Migrate disable support Dietmar Eggemann
2020-09-25 10:10   ` Peter Zijlstra
2020-09-25 11:58     ` Dietmar Eggemann
2020-09-25 12:19       ` Valentin Schneider
2020-09-25 17:49         ` Valentin Schneider
2020-09-29  9:15           ` Dietmar Eggemann
2020-09-25 18:17 ` Sebastian Andrzej Siewior
2020-09-25 19:32   ` Valentin Schneider
2020-10-02 14:30     ` Peter Zijlstra

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