Commit eb7a59b2 authored Feb 20, 2014 by Michael wang Committed by Thomas Gleixner Feb 21, 2014

sched/fair: Reset se-depth when task switched to FAIR



Sasha reported:

[  522.645288] BUG: unable to handle kernel NULL pointer dereference at ...
[  522.646271] IP: [<ffffffff81186c6f>] check_preempt_wakeup+0x11f/0x210
		...
[  522.650021] Call Trace:
[  522.650021]  <IRQ>
[  522.650021]  [<ffffffff8117361d>] check_preempt_curr+0x3d/0xb0
[  522.650021]  [<ffffffff81175d88>] ttwu_do_wakeup+0x18/0x130
		...

which was caused by the se-depth changed during the time when task is not
FAIR, and we will use the wrong depth value after it switched back to FAIR.

This patch reset the depth at the time when task switched to FAIR, make sure
that we always have the correct value when task is FAIR.

Cc: Ingo Molnar <mingo@kernel.org>
Reported-by: Sasha Levin <sasha.levin@oracle.com>
Tested-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Michael Wang <wangyun@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/5305732D.70001@linux.vnet.ibm.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

parent d97a860c

kernel/sched/fair.c

+9 −1

Original line number	Diff line number	Diff line
		@@ -7317,7 +7317,15 @@ static void switched_from_fair(struct rq rq, struct task_struct p)
		*/
		static void switched_to_fair(struct rq rq, struct task_struct p)
		{
		if (!p->se.on_rq)
		struct sched_entity *se = &p->se;
		#ifdef CONFIG_FAIR_GROUP_SCHED
		/*
		* Since the real-depth could have been changed (only FAIR
		* class maintain depth value), reset depth properly.
		*/
		se->depth = se->parent ? se->parent->depth + 1 : 0;
		#endif
		if (!se->on_rq)
		return;

		/*

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