Merge branch 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull a mutex fix from Ingo Molnar.

Fix the fastpath_lock failure contention flag for xchg-based mutexes.

* 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  mutex: Place lock in contended state after fastpath_lock failure

1 files changed, 9 insertions, 2 deletions

diff --git a/include/asm-generic/mutex-xchg.h b/include/asm-generic/mutex-xchg.h
index 580a6d35c700..c04e0db8a2d6 100644
--- a/include/asm-generic/mutex-xchg.h
+++ b/include/asm-generic/mutex-xchg.h
@@ -26,7 +26,13 @@ static inline void
 __mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
 {
         if (unlikely(atomic_xchg(count, 0) != 1))
-                fail_fn(count);
+                /*
+                 * We failed to acquire the lock, so mark it contended
+                 * to ensure that any waiting tasks are woken up by the
+                 * unlock slow path.
+                 */
+                if (likely(atomic_xchg(count, -1) != 1))
+                        fail_fn(count);
 }
 
 /**
@@ -43,7 +49,8 @@ static inline int
 __mutex_fastpath_lock_retval(atomic_t *count, int (*fail_fn)(atomic_t *))
 {
         if (unlikely(atomic_xchg(count, 0) != 1))
-                return fail_fn(count);
+                if (likely(atomic_xchg(count, -1) != 1))
+                        return fail_fn(count);
         return 0;
 }