nptl: Effectively skip CAS in spinlock loop

The commit:
"Add LLL_MUTEX_READ_LOCK [BZ #28537]"
SHA1: d672a98a1af106bd68deb15576710cd61363f7a6

introduced LLL_MUTEX_READ_LOCK, to skip CAS in spinlock loop
if atomic load fails. But, "continue" inside of do-while loop
does not skip the evaluation of escape expression, thus CAS
is not skipped.

Replace do-while with while and skip LLL_MUTEX_TRYLOCK if
LLL_MUTEX_READ_LOCK fails.

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
(cherry picked from commit 6b8dbbd03ac88f169b65b5c7d7278576a11d2e44)

diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c
index 2895926953eb7649bc2b032833a93472bd291c40..253743f76c1ade9261a06af00cb87cb5467a20ce 100644 (file)
--- a/nptl/pthread_mutex_lock.c
+++ b/nptl/pthread_mutex_lock.c
@@ -138,10 +138,9 @@ __pthread_mutex_lock (pthread_mutex_t *mutex)
                  break;
                }
              atomic_spin_nop ();
-             if (LLL_MUTEX_READ_LOCK (mutex) != 0)
-               continue;
            }
-         while (LLL_MUTEX_TRYLOCK (mutex) != 0);
+         while (LLL_MUTEX_READ_LOCK (mutex) != 0
+                || LLL_MUTEX_TRYLOCK (mutex) != 0);
 
          mutex->__data.__spins += (cnt - mutex->__data.__spins) / 8;
        }