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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>
This commit is contained in:
Juri Lelli 2014-10-24 10:16:38 +01:00 committed by Ingo Molnar
parent 64be6f1f5f
commit aee38ea954
1 changed files with 13 additions and 5 deletions
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18
kernel/sched/deadline.c
View File

@ -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();