Avoid extra load with CAS in __pthread_mutex_lock_full [BZ #28537]

Replace boolean CAS with value CAS to avoid the extra load.

Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
(cherry picked from commit 0b82747dc48d5bf0871bdc6da8cb6eec1256355f)

diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c
index 319658adc4e682ff7f2e5e9466a21b8f0dd1ceb8..0fd7467b97680bcd271d32fa529567205b4f0600 100644 (file)
--- a/nptl/pthread_mutex_lock.c
+++ b/nptl/pthread_mutex_lock.c
@@ -289,12 +289,12 @@ __pthread_mutex_lock_full (pthread_mutex_t *mutex)
             meantime.  */
          if ((oldval & FUTEX_WAITERS) == 0)
            {
-             if (atomic_compare_and_exchange_bool_acq (&mutex->__data.__lock,
-                                                       oldval | FUTEX_WAITERS,
-                                                       oldval)
-                 != 0)
+             int val;
+             if ((val = atomic_compare_and_exchange_val_acq
+                  (&mutex->__data.__lock, oldval | FUTEX_WAITERS,
+                   oldval)) != oldval)
                {
-                 oldval = mutex->__data.__lock;
+                 oldval = val;
                  continue;
                }
              oldval |= FUTEX_WAITERS;