[PATCH v3] nptl: Effectively skip CAS in spinlock loop

[Jangwoong Kim]

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.
---
 nptl/pthread_mutex_lock.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c
index 47b88a6b5b..06274c68e4 100644
--- a/nptl/pthread_mutex_lock.c
+++ b/nptl/pthread_mutex_lock.c
@@ -138,7 +138,7 @@ PTHREAD_MUTEX_LOCK (pthread_mutex_t *mutex)
 	  int cnt = 0;
 	  int max_cnt = MIN (max_adaptive_count (),
 			     mutex->__data.__spins * 2 + 10);
-	  do
+	  while (LLL_MUTEX_READ_LOCK (mutex) != 0 || LLL_MUTEX_TRYLOCK (mutex) != 0)
 	    {
 	      if (cnt++ >= max_cnt)
 		{
@@ -146,10 +146,7 @@ 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);
 
 	  mutex->__data.__spins += (cnt - mutex->__data.__spins) / 8;
 	}
-- 
2.25.1