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From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
To: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org
Subject: [PATCH] sched/fair: do not announce throttled next buddy in dequeue_task_fair
Date: Thu, 16 Jun 2016 15:57:15 +0300
Message-ID: <146608183552.21905.15924473394414832071.stgit@buzz> (raw)

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@yandex-team.ru>
Cc: Stable <stable@vger.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;

             reply index

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-16 12:57 Konstantin Khlebnikov [this message]
2016-06-16 17:06 ` bsegall
2016-06-21 13:44 ` Konstantin Khlebnikov
2016-06-24  9:00 ` [tip:sched/urgent] sched/fair: Do not announce throttled next buddy in dequeue_task_fair() tip-bot for Konstantin Khlebnikov
2016-07-11  7:25 ` [PATCH] sched/fair: do not announce throttled next buddy in dequeue_task_fair Wanpeng Li
2016-07-11  8:15   ` Konstantin Khlebnikov
2016-07-11  8:22   ` Xunlei Pang
2016-07-11  8:42     ` Xunlei Pang
2016-07-11  9:54       ` Wanpeng Li
2016-07-11 12:12         ` Xunlei Pang
2016-07-11 12:26           ` Konstantin Khlebnikov
2016-07-12 17:25             ` bsegall
2016-07-13  1:50               ` Wanpeng Li
2016-07-13  1:58                 ` Xunlei Pang
2016-07-13  2:14                   ` Wanpeng Li
2016-07-13 17:06                 ` bsegall
2016-07-14 12:11                   ` Wanpeng Li
2016-07-14 17:54                     ` bsegall
2016-07-14 22:30                       ` Wanpeng Li
2016-07-14 22:49                         ` bsegall
2016-07-14 23:03                           ` Wanpeng Li

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