[PATCH] sched/dl: Fix race between dl_task_timer() and sched_setaffinity()

[Kirill Tkhai <tkhai@yandex.ru>]

The race is in unlocked task_rq() access. In pair with parallel
call of sched_setaffinity() it may be a reason of corruption
of internal rq's data.

Signed-off-by: Kirill Tkhai <tkhai@yandex.ru>
CC: Juri Lelli <juri.lelli@gmail.com>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Ingo Molnar <mingo@redhat.com>
Cc: <stable@vger.kernel.org> # v3.14
---
 kernel/sched/deadline.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 800e99b..ffb023a 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -513,9 +513,16 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
 						     struct sched_dl_entity,
 						     dl_timer);
 	struct task_struct *p = dl_task_of(dl_se);
-	struct rq *rq = task_rq(p);
+	struct rq *rq;
+again:
+	rq = task_rq(p);
 	raw_spin_lock(&rq->lock);
 
+	if (unlikely(rq != task_rq(p))) {
+		raw_spin_unlock(&rq->lock);
+		goto again;
+	}
+
 	/*
 	 * We need to take care of a possible races here. In fact, the
 	 * task might have changed its scheduling policy to something