[PATCH RFC 05/33] locking/mutex: Change the atomic_dec_and_mutex_lock() return type

[Bart Van Assche]

Change the return type of atomic_dec_and_mutex_lock() from int into
bool. This will make it easier to add a thread-safety annotation to
this function. This patch does not change the behavior of any kernel
code because all atomic_dec_and_mutex_lock() callers either check whether
the return value of this function is zero or that it differs from zero.

This patch makes the atomic_dec_and_mutex_lock() signature consistent
with that of refcount_dec_and_mutex_lock().

Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
 Documentation/locking/mutex-design.rst | 2 +-
 include/linux/mutex.h                  | 2 +-
 kernel/locking/mutex.c                 | 8 ++++----
 3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/Documentation/locking/mutex-design.rst b/Documentation/locking/mutex-design.rst
index 7c30b4aa5e28..ec02e47b6e9e 100644
--- a/Documentation/locking/mutex-design.rst
+++ b/Documentation/locking/mutex-design.rst
@@ -144,7 +144,7 @@ Acquire the mutex, interruptible::
 
 Acquire the mutex, interruptible, if dec to 0::
 
-   int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
+   bool atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
 
 Unlock the mutex::
 
diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index 2bf91b57591b..6c0a8a843a29 100644
--- a/include/linux/mutex.h
+++ b/include/linux/mutex.h
@@ -196,7 +196,7 @@ extern void mutex_lock_io(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);
+bool atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
 
 DEFINE_GUARD(mutex, struct mutex *, mutex_lock(_T), mutex_unlock(_T))
 DEFINE_GUARD_COND(mutex, _try, mutex_trylock(_T))
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index b36f23de48f1..0af175f5f031 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -1118,19 +1118,19 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(contention_end);
  *
  * 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)
+bool 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;
+		return false;
 	/* 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;
+		return false;
 	}
 	/* we hit 0, and we hold the lock */
-	return 1;
+	return true;
 }
 EXPORT_SYMBOL(atomic_dec_and_mutex_lock);