Messages in this thread Patch in this message | | | From | Juri Lelli <> | Subject | [PATCH 4/4] sched/deadline: fix races between rt_mutex_setprio and dl_task_timer | Date | Fri, 24 Oct 2014 10:16:38 +0100 |
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dl_task_timer() is racy against several paths. Daniel noticed that the replenishment timer may experience a race condition against an enqueue_dl_entity() called from rt_mutex_setprio(). With his own words:
rt_mutex_setprio() resets p->dl.dl_throttled. So the pattern is: start_dl_timer() throttled = 1, rt_mutex_setprio() throlled = 0, sched_switch() -> enqueue_task(), dl_task_timer-> enqueue_task() throttled is 0
=> BUG_ON(on_dl_rq(dl_se)) fires as the scheduling entity is already enqueued on the -deadline runqueue.
As we do for the other races, we just bail out in the replenishment timer code.
Signed-off-by: Juri Lelli <juri.lelli@arm.com> Reported-by: Daniel Wagner <daniel.wagner@bmw-carit.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Juri Lelli <juri.lelli@gmail.com> Cc: Dario Faggioli <raistlin@linux.it> Cc: Michael Trimarchi <michael@amarulasolutions.com> Cc: Fabio Checconi <fchecconi@gmail.com> Cc: linux-kernel@vger.kernel.org --- kernel/sched/deadline.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index cf2c040..28d6088 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -518,12 +518,20 @@ again: } /* - * We need to take care of a possible races here. In fact, the - * task might have changed its scheduling policy to something - * different from SCHED_DEADLINE or changed its reservation - * parameters (through sched_setattr()). + * We need to take care of several possible races here: + * + * - the task might have changed its scheduling policy + * to something different than SCHED_DEADLINE + * - the task might have changed its reservation parameters + * (through sched_setattr()) + * - the task might have been boosted by someone else and + * might be in the boosting/deboosting path + * + * In all this cases we bail out, as the task is already + * in the runqueue or is going to be enqueued back anyway. */ - if (!dl_task(p) || dl_se->dl_new) + if (!dl_task(p) || dl_se->dl_new || + dl_se->dl_boosted || !dl_se->dl_throttled) goto unlock; sched_clock_tick(); -- 2.1.2
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