[tip:sched/core] sched: Do not attempt to destroy uninitialized rt_bandwidth

From: tip-bot for Bianca Lutz
Date: Thu Jul 21 2011 - 14:30:41 EST

Commit-ID: 99bc52429f11d1f4f81495ac8237085aaeb6bccf
Gitweb: http://git.kernel.org/tip/99bc52429f11d1f4f81495ac8237085aaeb6bccf
Author: Bianca Lutz <sowilo@xxxxxxxxxxxxxxx>
AuthorDate: Wed, 13 Jul 2011 20:13:36 +0200
Committer: Ingo Molnar <mingo@xxxxxxx>
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@xxxxxxxxxxxxxxx>
Signed-off-by: Jan Schoenherr <schnhrr@xxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Link: http://lkml.kernel.org/r/1310580816-10861-7-git-send-email-schnhrr@xxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
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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