[PATCH] cond_resched(): fix bogus might_sleep() warning

The BKS might be reacquired before we have dropped PREEMPT_ACTIVE, which
could trigger a second could trigger a second cond_resched() call.  Bug
found by Hirofumi Ogawa.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 5f2182d42241..4107db0dc091 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3877,6 +3877,13 @@ asmlinkage long sys_sched_yield(void)
 
 static inline void __cond_resched(void)
 {
+        /*
+         * The BKS might be reacquired before we have dropped
+         * PREEMPT_ACTIVE, which could trigger a second
+         * cond_resched() call.
+         */
+        if (unlikely(preempt_count()))
+                return;
         do {
                 add_preempt_count(PREEMPT_ACTIVE);
                 schedule();