19.05.2014, 17:11, "Juri Lelli" <juri.lelli@xxxxxxxxx>:
> On Sat, 17 May 2014 01:30:03 +0400
> Kirill Tkhai <tkhai@xxxxxxxxx> wrote:
>
>> The race is in unlocked task_rq() access. In pair with parallel
>> call of sched_setaffinity() it may be a reason of corruption
>> of internal rq's data.
>
> Sure, the thing can happen!
[snipped]
>> @@ -513,9 +513,16 @@ 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;
>
> We could maybe add a comment here, in line with what we have below, to
> document why we need this.
How about this? (I added comment and rewrote changelog).
[PATCH] sched/dl: Fix race between dl_task_timer() and sched_setaffinity()
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.
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(). This case is
an exception.
Signed-off-by: Kirill Tkhai <tkhai@xxxxxxxxx>
CC: Juri Lelli <juri.lelli@xxxxxxxxx>
CC: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CC: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v3.14
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 800e99b..c0a6921 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 (unlikely(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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