From: Valentin Schneider <valentin.schneider@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
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 11:07:47 +0100 [thread overview]
Message-ID: <jhj1riqmaoc.mognet@arm.com> (raw)
In-Reply-To: <20200925084339.GU2628@hirez.programming.kicks-ass.net>
On 25/09/20 09:43, Peter Zijlstra wrote:
> 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.
Makes sense, thanks.
next prev parent reply other threads:[~2020-09-25 10:07 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
2020-09-25 10:07 ` Valentin Schneider [this message]
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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