[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>

diff --git a/kernel/sched.c b/kernel/sched.c
index 5f2182d42241d20b41a12eb9da9671927b5b36d8..4107db0dc0919767b72b31e8dd88a5580294a578 100644 (file)
--- 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();