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authorKirill Tkhai <tkhai@yandex.ru>2014-05-20 13:33:42 +0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-06-11 11:54:11 -0700
commit8ac38a5e6c72bb5ad1607304a909332d2f460937 (patch)
tree5bd41e7c915ed7a1f8dacaddc8110bbd07da0850
parent1380335fc4c60decaee63e6c462267b0e134bd15 (diff)
sched/dl: Fix race in dl_task_timer()
commit 0f397f2c90ce68821ee864c2c53baafe78de765d upstream. Throttled task is still on rq, and it may be moved to other cpu if user is playing with sched_setaffinity(). Therefore, unlocked task_rq() access makes the race. Juri Lelli reports he got this race when dl_bandwidth_enabled() was not set. Other thing, pointed by Peter Zijlstra: "Now I suppose the problem can still actually happen when you change the root domain and trigger a effective affinity change that way". To fix that we do the same as made in __task_rq_lock(). We do not use __task_rq_lock() itself, because it has a useful lockdep check, which is not correct in case of dl_task_timer(). We do not need pi_lock locked here. This case is an exception (PeterZ): "The only reason we don't strictly need ->pi_lock now is because we're guaranteed to have p->state == TASK_RUNNING here and are thus free of ttwu races". Signed-off-by: Kirill Tkhai <tkhai@yandex.ru> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/3056991400578422@web14g.yandex.ru Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--kernel/sched/deadline.c10
1 files changed, 9 insertions, 1 deletions
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 6e79b3faa4cd..ce852643854b 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -490,9 +490,17 @@ 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 (rq != task_rq(p)) {
+ /* Task was moved, retrying. */
+ 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