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 5269b2d10ead09bc4d1386fac5c01f5a5df6ce78..d5786ca53aeb47d0be81e21825d049cf75363d93 100644 (file)
--- a/src/backend/storage/lmgr/lock.c
+++ b/src/backend/storage/lmgr/lock.c
@@ -646,7 +646,7 @@ 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));
@@ -1004,8 +1004,11 @@ RemoveLocalLock(LOCALLOCK *locallock)
                if (locallock->lockOwners[i].owner != NULL)
                        ResourceOwnerForgetLock(locallock->lockOwners[i].owner, 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))