Messages in this thread Patch in this message | | | Date | Thu, 5 Jun 2014 07:33:53 -0700 | From | tip-bot for Kirill Tkhai <> | Subject | [tip:sched/urgent] sched/dl: Fix race in dl_task_timer() |
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Commit-ID: 0f397f2c90ce68821ee864c2c53baafe78de765d Gitweb: http://git.kernel.org/tip/0f397f2c90ce68821ee864c2c53baafe78de765d Author: Kirill Tkhai <tkhai@yandex.ru> AuthorDate: Tue, 20 May 2014 13:33:42 +0400 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Thu, 5 Jun 2014 11:51:12 +0200
sched/dl: Fix race in dl_task_timer()
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: <stable@vger.kernel.org> # v3.14+ 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> --- kernel/sched/deadline.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 800e99b..14bc348 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -513,9 +513,17 @@ 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
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