Patch "sched/fair: Do not announce throttled next buddy in dequeue_task_fair()" has been added to the 4.4-stable tree

Patch "sched/fair: Do not announce throttled next buddy in dequeue_task_fair()" has been added to the 4.4-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    sched/fair: Do not announce throttled next buddy in dequeue_task_fair()

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     sched-fair-do-not-announce-throttled-next-buddy-in-dequeue_task_fair.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 754bd598be9bbc953bc709a9e8ed7f3188bfb9d7 Mon Sep 17 00:00:00 2001
From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Date: Thu, 16 Jun 2016 15:57:15 +0300
Subject: sched/fair: Do not announce throttled next buddy in dequeue_task_fair()

From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>

commit 754bd598be9bbc953bc709a9e8ed7f3188bfb9d7 upstream.

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

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ben Segall <bsegall@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/146608183552.21905.15924473394414832071.stgit@buzz
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Ben Pineau <benjamin.pineau@mirakl.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 kernel/sched/fair.c |    9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4233,15 +4233,14 @@ static void dequeue_task_fair(struct rq
 
 		/* 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;


Patches currently in stable-queue which might be from khlebnikov@yandex-team.ru are

queue-4.4/sched-fair-do-not-announce-throttled-next-buddy-in-dequeue_task_fair.patch
queue-4.4/sched-fair-initialize-throttle_count-for-new-task-groups-lazily.patch