Commit c5ae366e authored May 11, 2017 by Daniel Axtens Committed by Ingo Molnar Jun 20, 2017

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

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>

parent 6d3aed3d

kernel/sched/fair.c

+8 −2

Original line number	Diff line number	Diff line
		@@ -6164,18 +6164,24 @@ 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)
		{
		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)
		{