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authorJuri Lelli <juri.lelli@arm.com>2014-10-24 13:16:38 +0400
committerIngo Molnar <mingo@kernel.org>2014-10-28 12:46:01 +0300
commitaee38ea95419c818dfdde52b115aeffe9cbb259b (patch)
tree438cee90383ef1e33e33372f3a70b77a524a2e9b /kernel
parent64be6f1f5f710f5995d41caf8a1767fe6d2b5a87 (diff)
downloadlinux-aee38ea95419c818dfdde52b115aeffe9cbb259b.tar.xz
sched/deadline: Fix races between rt_mutex_setprio() and dl_task_timer()
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. Reported-by: Daniel Wagner <daniel.wagner@bmw-carit.de> Tested-by: Daniel Wagner <daniel.wagner@bmw-carit.de> Signed-off-by: Juri Lelli <juri.lelli@arm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: vincent@legout.info Cc: Dario Faggioli <raistlin@linux.it> Cc: Michael Trimarchi <michael@amarulasolutions.com> Cc: Fabio Checconi <fchecconi@gmail.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/1414142198-18552-5-git-send-email-juri.lelli@arm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched/deadline.c18
1 files changed, 13 insertions, 5 deletions
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 92279eaf0ef2..46167899d852 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();