linux-kernel - [PATCH 3/6] sched: Collate affine_move

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Message-ID: <20210224131355.500108964@infradead.org>
Date:   Wed, 24 Feb 2021 13:24:42 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Valentin Schneider <valentin.schneider@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Mel Gorman <mgorman@...e.de>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        linux-kernel@...r.kernel.org, peterz@...radead.org,
        Andi Kleen <andi@...stfloor.org>
Subject: [PATCH 3/6] sched: Collate affine_move_task() stoppers

The SCA_MIGRATE_ENABLE and task_running() cases are almost identical,
collapse them to avoid further duplication.

Fixes: 6d337eab041d ("sched: Fix migrate_disable() vs set_cpus_allowed_ptr()")
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/sched/core.c |   23 ++++++++---------------
 1 file changed, 8 insertions(+), 15 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2239,30 +2239,23 @@ static int affine_move_task(struct rq *r
 		return -EINVAL;
 	}
 
-	if (flags & SCA_MIGRATE_ENABLE) {
-
-		refcount_inc(&pending->refs); /* pending->{arg,stop_work} */
-		p->migration_flags &= ~MDF_PUSH;
-		task_rq_unlock(rq, p, rf);
-
-		stop_one_cpu_nowait(cpu_of(rq), migration_cpu_stop,
-				    &pending->arg, &pending->stop_work);
-
-		return 0;
-	}
-
 	if (task_running(rq, p) || p->state == TASK_WAKING) {
 		/*
-		 * Lessen races (and headaches) by delegating
-		 * is_migration_disabled(p) checks to the stopper, which will
-		 * run on the same CPU as said p.
+		 * MIGRATE_ENABLE gets here because 'p == current', but for
+		 * anything else we cannot do is_migration_disabled(), punt
+		 * and have the stopper function handle it all race-free.
 		 */
+
 		refcount_inc(&pending->refs); /* pending->{arg,stop_work} */
+		if (flags & SCA_MIGRATE_ENABLE)
+			p->migration_flags &= ~MDF_PUSH;
 		task_rq_unlock(rq, p, rf);
 
 		stop_one_cpu_nowait(cpu_of(rq), migration_cpu_stop,
 				    &pending->arg, &pending->stop_work);
 
+		if (flags & SCA_MIGRATE_ENABLE)
+			return 0;
 	} else {
 
 		if (!is_migration_disabled(p)) {