linux-kernel - [tip:sched/core] sched: Do not attempt to destroy uninitialized rt

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Message-ID: <tip-99bc52429f11d1f4f81495ac8237085aaeb6bccf@git.kernel.org>
Date:	Thu, 21 Jul 2011 18:30:11 GMT
From:	tip-bot for Bianca Lutz <sowilo@...tu-berlin.de>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	a.p.zijlstra@...llo.nl, schnhrr@...tu-berlin.de,
	sowilo@...tu-berlin.de, tglx@...utronix.de, mingo@...e.hu
Subject: [tip:sched/core] sched: Do not attempt to destroy uninitialized rt_bandwidth

Commit-ID:  99bc52429f11d1f4f81495ac8237085aaeb6bccf
Gitweb:     http://git.kernel.org/tip/99bc52429f11d1f4f81495ac8237085aaeb6bccf
Author:     Bianca Lutz <sowilo@...tu-berlin.de>
AuthorDate: Wed, 13 Jul 2011 20:13:36 +0200
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Thu, 21 Jul 2011 18:01:51 +0200

sched: Do not attempt to destroy uninitialized rt_bandwidth

If a task group is to be created and alloc_fair_sched_group() fails,
then the rt_bandwidth of the corresponding task group is not yet
initialized. The caller, sched_create_group(), starts a clean up
procedure which calls free_rt_sched_group() which unconditionally
destroys the not yet initialized rt_bandwidth.

This crashes or hangs the system in lock_hrtimer_base(): UP systems
dereference a NULL pointer, while SMP systems loop endlessly on a
condition that cannot become true.

This patch simply avoids the destruction of rt_bandwidth when the
initialization code path was not reached.

(This was discovered by accident with a custom kernel modification.)

Signed-off-by: Bianca Lutz <sowilo@...tu-berlin.de>
Signed-off-by: Jan Schoenherr <schnhrr@...tu-berlin.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Link: http://lkml.kernel.org/r/1310580816-10861-7-git-send-email-schnhrr@cs.tu-berlin.de
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/sched.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 3b3826e..f107204 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -8383,7 +8383,8 @@ static void free_rt_sched_group(struct task_group *tg)
 {
 	int i;
 
-	destroy_rt_bandwidth(&tg->rt_bandwidth);
+	if (tg->rt_se)
+		destroy_rt_bandwidth(&tg->rt_bandwidth);
 
 	for_each_possible_cpu(i) {
 		if (tg->rt_rq)
--
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