linux-kernel - [PATCH 6/6] sched: Do not attempt to destroy uninitialized rt

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Message-Id: <1310580816-10861-7-git-send-email-schnhrr@cs.tu-berlin.de>
Date:	Wed, 13 Jul 2011 20:13:36 +0200
From:	Jan H. Schönherr <schnhrr@...tu-berlin.de>
To:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, Bianca Lutz <sowilo@...tu-berlin.de>,
	Jan H. Schönherr <schnhrr@...tu-berlin.de>
Subject: [PATCH 6/6] sched: Do not attempt to destroy uninitialized rt_bandwidth

From: Bianca Lutz <sowilo@...tu-berlin.de>

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 H. Schönherr <schnhrr@...tu-berlin.de>
---
 kernel/sched.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 9a5f4c7..f29077c 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -8268,7 +8268,8 @@ 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)
-- 
1.7.3.4

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