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

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 1785acebf2ed14fd66955e2d9a55d77a025f418d), 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
index 8b5dcb82a81c06609750997acf8c9a6b8424142b..77de95d3593378eb6772cfff830aaf85705599b6 100644 (file)
--- 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))