[tip: sched/core] sched: Fix migration_cpu_stop() WARN

[tip-bot2 for Peter Zijlstra]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     1293771e4353c148d5f6908fb32d1c1cfd653e47
Gitweb:        https://git.kernel.org/tip/1293771e4353c148d5f6908fb32d1c1cfd653e47
Author:        Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate:    Tue, 17 Nov 2020 12:14:51 +01:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Thu, 19 Nov 2020 11:25:45 +01:00

sched: Fix migration_cpu_stop() WARN

Oleksandr reported hitting the WARN in the 'task_rq(p) != rq' branch
of migration_cpu_stop(). Valentin noted that using cpu_of(rq) in that
case is just plain wrong to begin with, since per the earlier branch
that isn't the actual CPU of the task.

Replace both instances of is_cpu_allowed() by a direct p->cpus_mask
test using task_cpu().

Reported-by: Oleksandr Natalenko <oleksandr@xxxxxxxxxxxxxx>
Debugged-by: Valentin Schneider <valentin.schneider@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 kernel/sched/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4d1fd4b..28d541a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1911,7 +1911,7 @@ static int migration_cpu_stop(void *data)
 			 * and we should be valid again. Nothing to do.
 			 */
 			if (!pending) {
-				WARN_ON_ONCE(!is_cpu_allowed(p, cpu_of(rq)));
+				WARN_ON_ONCE(!cpumask_test_cpu(task_cpu(p), &p->cpus_mask));
 				goto out;
 			}
 
@@ -1950,7 +1950,7 @@ static int migration_cpu_stop(void *data)
 		 * valid again. Nothing to do.
 		 */
 		if (!pending) {
-			WARN_ON_ONCE(!is_cpu_allowed(p, cpu_of(rq)));
+			WARN_ON_ONCE(!cpumask_test_cpu(task_cpu(p), &p->cpus_mask));
 			goto out;
 		}