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Date:   Mon, 01 Mar 2021 10:16:17 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@linutronix.de>
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Subject: [tip: sched/urgent] sched: Collate affine_move_task() stoppers
Cc:     stable@kernel.org, "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Valentin Schneider <valentin.schneider@arm.com>,
        x86@kernel.org, linux-kernel@vger.kernel.org
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The following commit has been merged into the sched/urgent branch of tip:

Commit-ID:     dbf983c0a5c37da2d476564792bd84e0e8f067fc
Gitweb:        https://git.kernel.org/tip/dbf983c0a5c37da2d476564792bd84e0e8f067fc
Author:        Peter Zijlstra <peterz@infradead.org>
AuthorDate:    Wed, 24 Feb 2021 11:15:23 +01:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Mon, 01 Mar 2021 11:02:14 +01:00

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()")
Cc: stable@kernel.org
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Link: https://lkml.kernel.org/r/20210224131355.500108964@infradead.org
---
 kernel/sched/core.c | 23 ++++++++---------------
 1 file changed, 8 insertions(+), 15 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 088e8f4..84b657f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2239,30 +2239,23 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag
 		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)) {