linux-kernel - [PATCH] sched/dl: Fix race between dl_task_timer() and sched

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Message-ID: <20140516213003.10384.7946.stgit@localhost>
Date:	Sat, 17 May 2014 01:30:03 +0400
From:	Kirill Tkhai <tkhai@...dex.ru>
To:	linux-kernel@...r.kernel.org
Cc:	peterz@...radead.org, tkhai@...dex.ru, mingo@...hat.com,
	stable@...r.kernel.org, juri.lelli@...il.com
Subject: [PATCH] sched/dl: Fix race between dl_task_timer() and
 sched_setaffinity()

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@...dex.ru>
CC: Juri Lelli <juri.lelli@...il.com>
CC: Peter Zijlstra <peterz@...radead.org>
CC: Ingo Molnar <mingo@...hat.com>
Cc: <stable@...r.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

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