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 11:56:15 +0200 [thread overview]
Message-ID: <20200925095615.GA2651@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200925090528.GV2628@hirez.programming.kicks-ass.net>
On Fri, Sep 25, 2020 at 11:05:28AM +0200, Peter Zijlstra wrote:
> On Thu, Sep 24, 2020 at 08:59:33PM +0100, Valentin Schneider wrote:
> > > @@ -2025,19 +2138,8 @@ static int __set_cpus_allowed_ptr(struct
> > > if (cpumask_test_cpu(task_cpu(p), new_mask))
> > > goto out;
> >
> > I think this needs a cancellation of any potential pending migration
> > requests. Consider a task P0 running on CPU0:
> >
> > P0 P1 P2
> >
> > migrate_disable();
> > <preempt>
> > set_cpus_allowed_ptr(P0, CPU1);
> > // waits for completion
> > set_cpus_allowed_ptr(P0, CPU0);
> > // Already good, no waiting for completion
> > <resumes>
> > migrate_enable();
> > // task_cpu(p) allowed, no move_task()
> >
> > AIUI in this scenario P1 would stay forever waiting.
>
> The other approach is trying to handle that last condition in
> move_task(), but I'm quite sure that's going to be aweful too :/
Something like so perhaps?
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2039,6 +2039,10 @@ static int move_task(struct rq *rq, stru
if (WARN_ON_ONCE(!pending))
return -EINVAL;
+ /* Can the task run on the task's current CPU? If so, we're done */
+ if (cpumask_test_cpu(task_cpu(p), &p->cpus_mask))
+ goto easy;
+
arg.done = &pending->done;
if (flags & SCA_MIGRATE_ENABLE) {
@@ -2063,6 +2067,7 @@ static int move_task(struct rq *rq, stru
if (task_on_rq_queued(p))
rq = move_queued_task(rq, rf, p, dest_cpu);
+easy:
p->migration_pending = NULL;
complete = true;
}
@@ -2151,10 +2156,6 @@ static int __set_cpus_allowed_ptr(struct
p->nr_cpus_allowed != 1);
}
- /* Can the task run on the task's current CPU? If so, we're done */
- if (cpumask_test_cpu(task_cpu(p), new_mask))
- goto out;
-
return move_task(rq, &rf, p, dest_cpu, flags);
out:
next prev parent reply other threads:[~2020-09-25 9:56 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
2020-09-25 9:05 ` Peter Zijlstra
2020-09-25 9:56 ` Peter Zijlstra [this message]
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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