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authorEric Paris <eparis@redhat.com>2009-03-23 18:22:09 +0100
committerIngo Molnar <mingo@elte.hu>2009-04-29 16:45:54 +0200
commitb1fca26631f76a5e8b18435a43f5d82b8734da4b (patch)
tree6b8e651239219e85a6b3b9238878c4a6eb4f2d9c
parent56a50adda49b2020156616c4eb15353e0f9ad7de (diff)
mutex: add atomic_dec_and_mutex_lock()
Much like the atomic_dec_and_lock() function in which we take an hold a spin_lock if we drop the atomic to 0 this function takes and holds the mutex if we dec the atomic to 0. Signed-off-by: Eric Paris <eparis@redhat.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Paul Mackerras <paulus@samba.org> Orig-LKML-Reference: <20090323172417.410913479@chello.nl> Signed-off-by: Ingo Molnar <mingo@elte.hu>
-rw-r--r--include/linux/mutex.h23
1 files changed, 23 insertions, 0 deletions
diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index 3069ec7e0ab..93054fc3635 100644
--- a/include/linux/mutex.h
+++ b/include/linux/mutex.h
@@ -151,4 +151,27 @@ extern int __must_check mutex_lock_killable(struct mutex *lock);
extern int mutex_trylock(struct mutex *lock);
extern void mutex_unlock(struct mutex *lock);
+/**
+ * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0
+ * @cnt: the atomic which we are to dec
+ * @lock: the mutex to return holding if we dec to 0
+ *
+ * return true and hold lock if we dec to 0, return false otherwise
+ */
+static inline int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock)
+{
+ /* dec if we can't possibly hit 0 */
+ if (atomic_add_unless(cnt, -1, 1))
+ return 0;
+ /* we might hit 0, so take the lock */
+ mutex_lock(lock);
+ if (!atomic_dec_and_test(cnt)) {
+ /* when we actually did the dec, we didn't hit 0 */
+ mutex_unlock(lock);
+ return 0;
+ }
+ /* we hit 0, and we hold the lock */
+ return 1;
+}
+
#endif