Eric Lee / smarc-ti-linux-kernel

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Commit 8ac38a5e6c72bb5ad1607304a909332d2f460937

Authored by Kirill Tkhai
Committed by Greg Kroah-Hartman
1 parent 1380335fc4
Exists in ti-linux-3.14.y and in 2 other branches processor-sdk-linux-01.00.00, smarc-ti-linux-3.14.y

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>

Showing 1 changed file with 9 additions and 1 deletions Side-by-side Diff

kernel/sched/deadline.c
Diff comments   View file @ 8ac38a5
... ... @@ -490,8 +490,16 @@
490 490 struct sched_dl_entity,
491 491 dl_timer);
492 492 struct task_struct *p = dl_task_of(dl_se);
493   - struct rq *rq = task_rq(p);
  493 + struct rq *rq;
  494 +again:
  495 + rq = task_rq(p);
494 496 raw_spin_lock(&rq->lock);
  497 +
  498 + if (rq != task_rq(p)) {
  499 + /* Task was moved, retrying. */
  500 + raw_spin_unlock(&rq->lock);
  501 + goto again;
  502 + }
495 503  
496 504 /*
497 505 * We need to take care of a possible races here. In fact, the