commit 43760d33d78f9ea8c8af942b570112ee801b99df

Author: Jangwoong Kim <6812skiii@gmail.com>

Date:   Tue Dec 14 21:30:51 2021 +0900

    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 49901ffa0a96d659..bbe754a272b97d91 100644

--- a/nptl/pthread_mutex_lock.c

+++ b/nptl/pthread_mutex_lock.c

@@ -147,10 +147,9 @@ 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;

 	}