Merge pull request #2670 from wiredtiger/wt-2566mongodb-3.3.5

WT-2566 Lock/unlock operations should imply memory barriers.
(cherry picked from commit 05cfbc26c2ab2099d7c98080a79ae67ea531c24f)

1 files changed, 12 insertions, 0 deletions

diff --git a/src/include/mutex.i b/src/include/mutex.i
index 52250f84ab3..65956c13c08 100644
--- a/src/include/mutex.i
+++ b/src/include/mutex.i
@@ -306,6 +306,12 @@ __wt_fair_lock(WT_SESSION_IMPL *session, WT_FAIR_LOCK *lock)
 			__wt_sleep(0, 10);
 	}
 
+	/*
+	 * Applications depend on a barrier here so that operations holding the
+	 * lock see consistent data.
+	 */
+	WT_READ_BARRIER();
+
 	return (0);
 }
 
@@ -319,6 +325,12 @@ __wt_fair_unlock(WT_SESSION_IMPL *session, WT_FAIR_LOCK *lock)
 	WT_UNUSED(session);
 
 	/*
+	 * Ensure that all updates made while the lock was held are visible to
+	 * the next thread to acquire the lock.
+	 */
+	WT_WRITE_BARRIER();
+
+	/*
 	 * We have exclusive access - the update does not need to be atomic.
 	 */
 	++lock->fair_lock_owner;