linux-kernel - [PATCH] sched/fair: do not announce throttled next buddy in dequeue_task

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Date:	Thu, 16 Jun 2016 15:57:15 +0300
From:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Cc:	stable@...r.kernel.org
Subject: [PATCH] sched/fair: do not announce throttled next buddy in
 dequeue_task_fair

Hierarchy could be already throttled at this point. Throttled next
buddy could trigger null pointer dereference in pick_next_task_fair().

Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc: Stable <stable@...r.kernel.org> # v3.2+
---
 kernel/sched/fair.c |    9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index fe809fe169d2..3c6b038cb734 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4519,15 +4519,14 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 
 		/* Don't dequeue parent if it has other entities besides us */
 		if (cfs_rq->load.weight) {
+			/* avoid re-evaluating load for this entity */
+			se = parent_entity(se);
 			/*
 			 * Bias pick_next to pick a task from this cfs_rq, as
 			 * p is sleeping when it is within its sched_slice.
 			 */
-			if (task_sleep && parent_entity(se))
-				set_next_buddy(parent_entity(se));
-
-			/* avoid re-evaluating load for this entity */
-			se = parent_entity(se);
+			if (task_sleep && se && !throttled_hierarchy(cfs_rq))
+				set_next_buddy(se);
 			break;
 		}
 		flags |= DEQUEUE_SLEEP;