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From: Peter Zijlstra <peterz@infradead.org>
To: Valentin Schneider <valentin.schneider@arm.com>
Cc: linux-kernel@vger.kernel.org, Will Deacon <will@kernel.org>,
	Ingo Molnar <mingo@kernel.org>,
	Morten Rasmussen <morten.rasmussen@arm.com>,
	Qais Yousef <qais.yousef@arm.com>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Quentin Perret <qperret@google.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	kernel-team@android.com
Subject: Re: [PATCH 2/2] sched: Plug race between SCA, hotplug and migration_cpu_stop()
Date: Thu, 27 May 2021 11:12:22 +0200	[thread overview]
Message-ID: <YK9idgafP4G/ECme@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210526205751.842360-3-valentin.schneider@arm.com>

On Wed, May 26, 2021 at 09:57:51PM +0100, Valentin Schneider wrote:

> -			rq = __migrate_task(rq, &rf, p, arg->dest_cpu);

Suggests we ought to at the very least include something like the below.

/me continues reading...

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2246,28 +2246,6 @@ struct set_affinity_pending {
 	struct migration_arg	arg;
 };
 
-/*
- * Move (not current) task off this CPU, onto the destination CPU. We're doing
- * this because either it can't run here any more (set_cpus_allowed()
- * away from this CPU, or CPU going down), or because we're
- * attempting to rebalance this task on exec (sched_exec).
- *
- * So we race with normal scheduler movements, but that's OK, as long
- * as the task is no longer on this CPU.
- */
-static struct rq *__migrate_task(struct rq *rq, struct rq_flags *rf,
-				 struct task_struct *p, int dest_cpu)
-{
-	/* Affinity changed (again). */
-	if (!is_cpu_allowed(p, dest_cpu))
-		return rq;
-
-	update_rq_clock(rq);
-	rq = move_queued_task(rq, rf, p, dest_cpu);
-
-	return rq;
-}
-
 static int select_fallback_rq(int cpu, struct task_struct *p);
 
 /*
@@ -2292,7 +2270,7 @@ static int migration_cpu_stop(void *data
 	local_irq_save(rf.flags);
 	/*
 	 * We need to explicitly wake pending tasks before running
-	 * __migrate_task() such that we will not miss enforcing cpus_ptr
+	 * move_queued_task() such that we will not miss enforcing cpus_ptr
 	 * during wakeups, see set_cpus_allowed_ptr()'s TASK_WAKING test.
 	 */
 	flush_smp_call_function_from_idle();
@@ -8463,7 +8441,7 @@ static int __balance_push_cpu_stop(void
 
 	if (task_rq(p) == rq && task_on_rq_queued(p)) {
 		cpu = select_fallback_rq(rq->cpu, p);
-		rq = __migrate_task(rq, &rf, p, cpu);
+		rq = move_queued_task(rq, &rf, p, cpu);
 	}
 
 	rq_unlock(rq, &rf);

  reply	other threads:[~2021-05-27  9:12 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-26 20:57 [PATCH 0/2] sched: SCA vs hotplug vs stopper races fixes Valentin Schneider
2021-05-26 20:57 ` [PATCH 1/2] sched: Don't defer CPU pick to migration_cpu_stop() Valentin Schneider
2021-06-01 14:04   ` [tip: sched/core] " tip-bot2 for Valentin Schneider
2021-05-26 20:57 ` [PATCH 2/2] sched: Plug race between SCA, hotplug and migration_cpu_stop() Valentin Schneider
2021-05-27  9:12   ` Peter Zijlstra [this message]
2021-06-01 16:59   ` Valentin Schneider
2021-06-02 15:26     ` Will Deacon
2021-06-02 19:43       ` Valentin Schneider
2021-06-22 13:51         ` Will Deacon
2021-06-24  9:33           ` Valentin Schneider

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