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 1eb2d4b68da5bf1a5ee218f8e14535139f4f4c33..c377d384b765a7efa1d9483d53fe7f5855e1f42a 100644 (file)
--- a/src/backend/storage/lmgr/lock.c
+++ b/src/backend/storage/lmgr/lock.c
@@ -753,7 +753,7 @@ LockAcquireExtended(const LOCKTAG *locktag,
                locallock->numLockOwners = 0;
                locallock->maxLockOwners = 8;
                locallock->holdsStrongLockCount = FALSE;
-               locallock->lockOwners = NULL;
+               locallock->lockOwners = NULL;   /* in case next line fails */
                locallock->lockOwners = (LOCALLOCKOWNER *)
                        MemoryContextAlloc(TopMemoryContext,
                                                  locallock->maxLockOwners * sizeof(LOCALLOCKOWNER));
@@ -1222,7 +1222,9 @@ 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 (locallock->holdsStrongLockCount)