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sched/fair: WARN() and refuse to set buddy when !se->on_rq

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If we set a next or last buddy for a se that is not on_rq, we will
end up taking a NULL pointer dereference in wakeup_preempt_entity
via pick_next_task_fair.

Detect when we would be about to do that, throw a warning and
then refuse to actually set it.

This has been suggested at least twice:

  https://marc.info/?l=linux-kernel&m=146651668921468&w=2
  https://lkml.org/lkml/2016/6/16/663

I recently had to debug a problem with these (we hadn't backported
Konstantin's patches in this area) and this would have saved a lot
of time/pain.

Just do it.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Cc: Ben Segall <bsegall@google.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170510201139.16236-1-dja@axtens.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Daniel Axtens 2017-05-11 06:11:39 +10:00 committed by Ingo Molnar
parent 6d3aed3d8a
commit c5ae366e12
1 changed files with 8 additions and 2 deletions
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10
kernel/sched/fair.c
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@ -6164,8 +6164,11 @@ static void set_last_buddy(struct sched_entity *se)
if (entity_is_task(se) && unlikely(task_of(se)->policy == SCHED_IDLE))
return;
for_each_sched_entity(se)
for_each_sched_entity(se) {
if (SCHED_WARN_ON(!se->on_rq))
return;
cfs_rq_of(se)->last = se;
}
}
static void set_next_buddy(struct sched_entity *se)
@ -6173,8 +6176,11 @@ static void set_next_buddy(struct sched_entity *se)
if (entity_is_task(se) && unlikely(task_of(se)->policy == SCHED_IDLE))
return;
for_each_sched_entity(se)
for_each_sched_entity(se) {
if (SCHED_WARN_ON(!se->on_rq))
return;
cfs_rq_of(se)->next = se;
}
}
static void set_skip_buddy(struct sched_entity *se)