[PATCH] sched/deadline: Use task_on_rq_migrating() helper

[luoliang]

From: Liang Luo <luoliang@xxxxxxxxxx>

Replace the open-coded "p->on_rq == TASK_ON_RQ_MIGRATING" comparisons
in enqueue_task_dl() and dequeue_task_dl() with the existing
task_on_rq_migrating() helper, consistent with the rest of the
scheduler code.

The helper uses READ_ONCE() when loading ->on_rq, which was added by
commit c546951d9c93 ("sched/core: Use READ_ONCE()/WRITE_ONCE() in
move_queued_task()/task_rq_lock()") for LKMM compliance.  As documented
in that commit, move_queued_task() synchronizes with task_rq_lock():

  move_queued_task()                task_rq_lock()
  [S] ->on_rq = MIGRATING          [L] rq = task_rq()
  WMB (__set_task_cpu())           ACQUIRE (rq->lock)
  [S] ->cpu = new_cpu              [L] ->on_rq

The READ_ONCE() on the ->on_rq load ensures proper pairing with the
WRITE_ONCE() on the writer side.  The open-coded checks in deadline.c
lack this annotation.

No functional change.

Signed-off-by: Liang Luo <luoliang@xxxxxxxxxx>
---
 kernel/sched/deadline.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 7db4c87df83b..9d2c42b8661f 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -2335,7 +2335,7 @@ static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags)
 	check_schedstat_required();
 	update_stats_wait_start_dl(dl_rq_of_se(&p->dl), &p->dl);
 
-	if (p->on_rq == TASK_ON_RQ_MIGRATING)
+	if (task_on_rq_migrating(p))
 		flags |= ENQUEUE_MIGRATING;
 
 	enqueue_dl_entity(&p->dl, flags);
@@ -2354,7 +2354,7 @@ static bool dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags)
 {
 	update_curr_dl(rq);
 
-	if (p->on_rq == TASK_ON_RQ_MIGRATING)
+	if (task_on_rq_migrating(p))
 		flags |= DEQUEUE_MIGRATING;
 
 	dequeue_dl_entity(&p->dl, flags);
-- 
2.25.1