4 files changed, 30 insertions, 5 deletions

diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index 3069ec7e0ab8..878cab4f5fcc 100644
--- a/include/linux/mutex.h
+++ b/include/linux/mutex.h
@@ -150,5 +150,6 @@ extern int __must_check mutex_lock_killable(struct mutex *lock);
  */
 extern int mutex_trylock(struct mutex *lock);
 extern void mutex_unlock(struct mutex *lock);
+extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
 
 #endif
diff --git a/include/linux/spinlock_up.h b/include/linux/spinlock_up.h
index 938234c4a996..d4841ed8215b 100644
--- a/include/linux/spinlock_up.h
+++ b/include/linux/spinlock_up.h
@@ -60,6 +60,7 @@ static inline void __raw_spin_unlock(raw_spinlock_t *lock)
 #define __raw_spin_is_locked(lock)      ((void)(lock), 0)
 /* for sched.c and kernel_lock.c: */
 # define __raw_spin_lock(lock)          do { (void)(lock); } while (0)
+# define __raw_spin_lock_flags(lock, flags)     do { (void)(lock); } while (0)
 # define __raw_spin_unlock(lock)        do { (void)(lock); } while (0)
 # define __raw_spin_trylock(lock)       ({ (void)(lock); 1; })
 #endif /* DEBUG_SPINLOCK */
diff --git a/kernel/mutex.c b/kernel/mutex.c
index 6ca5fe96e393..e5cc0cd28d54 100644
--- a/kernel/mutex.c
+++ b/kernel/mutex.c
@@ -473,5 +473,28 @@ int __sched mutex_trylock(struct mutex *lock)
 
         return ret;
 }
-
 EXPORT_SYMBOL(mutex_trylock);
+
+/**
+ * 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
+ */
+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;
+}
+EXPORT_SYMBOL(atomic_dec_and_mutex_lock);
diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c
index fec77e7e0562..820c5af44f3e 100644
--- a/kernel/rtmutex.c
+++ b/kernel/rtmutex.c
@@ -891,9 +891,9 @@ int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock,
 EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
 
 /**
- * rt_mutex_lock_interruptible_ktime - lock a rt_mutex interruptible
- *                                     the timeout structure is provided
- *                                     by the caller
+ * rt_mutex_timed_lock - lock a rt_mutex interruptible
+ *                      the timeout structure is provided
+ *                      by the caller
  *
  * @lock:               the rt_mutex to be locked
  * @timeout:            timeout structure or NULL (no timeout)
@@ -940,7 +940,7 @@ void __sched rt_mutex_unlock(struct rt_mutex *lock)
 }
 EXPORT_SYMBOL_GPL(rt_mutex_unlock);
 
-/***
+/**
  * rt_mutex_destroy - mark a mutex unusable
  * @lock: the mutex to be destroyed
  *