[PATCH RT 3/8] sched: Collate affine_move_task() stoppers

[Steven Rostedt]

5.10.47-rt46-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

commit 58b1a45086b5f80f2b2842aa7ed0da51a64a302b upstream.

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@xxxxxxxxxx
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Reviewed-by: Valentin Schneider <valentin.schneider@xxxxxxx>
Link: https://lkml.kernel.org/r/20210224131355.500108964@xxxxxxxxxxxxx
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
---
 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 d497b13efb53..6880c300c624 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2275,30 +2275,23 @@ 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)) {
-- 
2.30.2