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Commit 5238cdd3 authored by Paul Turner's avatar Paul Turner Committed by Ingo Molnar
Browse files

sched: Prevent buddy interactions with throttled entities 



Buddies allow us to select "on-rq" entities without actually selecting them
from a cfs_rq's rb_tree.  As a result we must ensure that throttled entities
are not falsely nominated as buddies.  The fact that entities are dequeued
within throttle_entity is not sufficient for clearing buddy status as the
nomination may occur after throttling.

Signed-off-by: default avatarPaul Turner <pjt@google.com>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20110721184757.886850167@google.com


Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 64660c86

kernel/sched_fair.c

+17 −1
Original line number Diff line number Diff line
@@ -2348,6 +2348,15 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_ 
	if (unlikely(se == pse))

		return;



	/*

	 * This is possible from callers such as pull_task(), in which we

	 * unconditionally check_prempt_curr() after an enqueue (which may have

	 * lead to a throttle).  This both saves work and prevents false

	 * next-buddy nomination below.

	 */

	if (unlikely(throttled_hierarchy(cfs_rq_of(pse))))

		return;



	if (sched_feat(NEXT_BUDDY) && scale && !(wake_flags & WF_FORK)) {

		set_next_buddy(pse);

		next_buddy_marked = 1;
@@ -2356,6 +2365,12 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_ 
	/*

	 * We can come here with TIF_NEED_RESCHED already set from new task

	 * wake up path.

	 *

	 * Note: this also catches the edge-case of curr being in a throttled

	 * group (e.g. via set_curr_task), since update_curr() (in the

	 * enqueue of curr) will have resulted in resched being set.  This

	 * prevents us from potentially nominating it as a false LAST_BUDDY

	 * below.

	 */

	if (test_tsk_need_resched(curr))

		return;
@@ -2474,7 +2489,8 @@ static bool yield_to_task_fair(struct rq *rq, struct task_struct *p, bool preemp 
{

	struct sched_entity *se = &p->se;



	if (!se->on_rq)

	/* throttled hierarchies are not runnable */

	if (!se->on_rq || throttled_hierarchy(cfs_rq_of(se)))

		return false;



	/* Tell the scheduler that we'd really like pse to run next. */