Commit-ID: 9ab772cd535c4b256a577eae516f9c7462346b2d
Gitweb: http://git.kernel.org/tip/9ab772cd535c4b256a577eae516f9c7462346b2d
Author: Eric Paris <eparis@xxxxxxxxxx>
AuthorDate: Mon, 23 Mar 2009 18:22:09 +0100
Committer: Ingo Molnar <mingo@xxxxxxx>
CommitDate: Mon, 6 Apr 2009 09:30:26 +0200
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@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Orig-LKML-Reference: <20090323172417.410913479@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
include/linux/mutex.h | 23 +++++++++++++++++++++++
1 files changed, 23 insertions(+), 0 deletions(-)
diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index 3069ec7..93054fc 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
--
To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
|