Be more wary about partially-valid LOCALLOCK data in RemoveLocalLock().

tglsfdc · tglsfdc · commit eed5bbc48026 · 2015-09-20T16:48:44.000-04:00
RemoveLocalLock() must consider the possibility that LockAcquireExtended() failed to palloc the initial space for a locallock's lockOwners array. I had evidently meant to cope with this hazard when the code was originally written (commit 1785ace), but missed that the pfree needed to be protected with an if-test. Just to make sure things are left in a clean state, reset numLockOwners as well. Per low-memory testing by Andreas Seltenreich. Back-patch to all supported branches.
diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c
@@ -644,7 +644,7 @@ LockAcquireExtended(const LOCKTAG *locktag,
 		locallock->nLocks = 0;
 		locallock->numLockOwners = 0;
 		locallock->maxLockOwners = 8;
-		locallock->lockOwners = NULL;
+		locallock->lockOwners = NULL;	/* in case next line fails */
 		locallock->lockOwners = (LOCALLOCKOWNER *)
 			MemoryContextAlloc(TopMemoryContext,
 						  locallock->maxLockOwners * sizeof(LOCALLOCKOWNER));
@@ -994,8 +994,11 @@ LockAcquireExtended(const LOCKTAG *locktag,
 static void
 RemoveLocalLock(LOCALLOCK *locallock)
 {
-	pfree(locallock->lockOwners);
+	locallock->numLockOwners = 0;
+	if (locallock->lockOwners != NULL)
+		pfree(locallock->lockOwners);
 	locallock->lockOwners = NULL;
+
 	if (!hash_search(LockMethodLocalHash,
 					 (void *) &(locallock->tag),
 					 HASH_REMOVE, NULL))
