[tip: sched/core] sched: Use WRITE_ONCE() for p->on_rq

[tip-bot2 for Paul E. McKenney]

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

Commit-ID:     d6111cf45c5787282b2e20d77bdb6b28881d516a
Gitweb:        https://git.kernel.org/tip/d6111cf45c5787282b2e20d77bdb6b28881d516a
Author:        Paul E. McKenney <paulmck@xxxxxxxxxx>
AuthorDate:    Tue, 31 Oct 2023 11:12:01 -07:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Wed, 15 Nov 2023 09:57:45 +01:00

sched: Use WRITE_ONCE() for p->on_rq

Since RCU-tasks uses READ_ONCE(p->on_rq), ensure the write-side
matches with WRITE_ONCE().

Signed-off-by: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/e4896e0b-eacc-45a2-a7a8-de2280a51ecc@paulmck-laptop
---
 kernel/sched/core.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a708d22..9d5099d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2124,12 +2124,14 @@ void activate_task(struct rq *rq, struct task_struct *p, int flags)
 
 	enqueue_task(rq, p, flags);
 
-	p->on_rq = TASK_ON_RQ_QUEUED;
+	WRITE_ONCE(p->on_rq, TASK_ON_RQ_QUEUED);
+	ASSERT_EXCLUSIVE_WRITER(p->on_rq);
 }
 
 void deactivate_task(struct rq *rq, struct task_struct *p, int flags)
 {
-	p->on_rq = (flags & DEQUEUE_SLEEP) ? 0 : TASK_ON_RQ_MIGRATING;
+	WRITE_ONCE(p->on_rq, (flags & DEQUEUE_SLEEP) ? 0 : TASK_ON_RQ_MIGRATING);
+	ASSERT_EXCLUSIVE_WRITER(p->on_rq);
 
 	dequeue_task(rq, p, flags);
 }