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@cs.tu-berlin.de>
Signed-off-by: Jan Schoenherr <schnhrr@cs.tu-berlin.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1310580816-10861-7-git-send-email-schnhrr@cs.tu-berlin.de
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 2 insertions, 1 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 3b3826ebe793..f107204db53f 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)