diff --git a/lustre/ChangeLog b/lustre/ChangeLog
index 7b6315a629248553c69e71b03813f73a7f4320f7..c79cb6a0ddf24bfb5bc09e0db2bc9b1873f82647 100644
--- a/lustre/ChangeLog
+++ b/lustre/ChangeLog
@@ -24,6 +24,12 @@ tbd Sun Microsystems, Inc.
 	  	'tunefs.lustre --param="mdt.quota_type=ug1" $MDTDEV'.
 	  For more information, please refer to bugzilla 13904.
 
+Severity   : major
+Bugzilla   : 15924
+Description: do not process already freed flock
+Details    : flock can possibly be freed by another thread before it reaches
+             to ldlm_flock_completion_ast.
+
 Severity   : normal
 Bugzilla   : 14480
 Description: LBUG during stress test
diff --git a/lustre/ldlm/ldlm_flock.c b/lustre/ldlm/ldlm_flock.c
index 0b9f09b8170af752748bbf3762557f80f67f008c..dddd257f16500145afbb6daa403a8badbd41efa1 100644
--- a/lustre/ldlm/ldlm_flock.c
+++ b/lustre/ldlm/ldlm_flock.c
@@ -544,6 +544,13 @@ ldlm_flock_completion_ast(struct ldlm_lock *lock, int flags, void *data)
         RETURN(rc);
  
 granted:
+        /* before flock's complete ast gets here, the flock
+         * can possibly be freed by another thread
+         */
+        if (lock->l_destroyed) {
+                LDLM_DEBUG(lock, "already destroyed by another thread");
+                RETURN(0);
+        }
 
         LDLM_DEBUG(lock, "client-side enqueue granted");
         ns = lock->l_resource->lr_namespace;