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

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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 1785acebf2), 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.
This commit is contained in:
Tom Lane 2015-09-20 16:48:44 -04:00
parent 44297a058e
commit eed5bbc480
1 changed files with 5 additions and 2 deletions
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7
src/backend/storage/lmgr/lock.c
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@ -644,7 +644,7 @@ LockAcquireExtended(const LOCKTAG *locktag,
locallock->nLocks = 0; locallock->nLocks = 0;
locallock->numLockOwners = 0; locallock->numLockOwners = 0;
locallock->maxLockOwners = 8; locallock->maxLockOwners = 8;
locallock->lockOwners = NULL; locallock->lockOwners = NULL; /* in case next line fails */
locallock->lockOwners = (LOCALLOCKOWNER *) locallock->lockOwners = (LOCALLOCKOWNER *)
MemoryContextAlloc(TopMemoryContext, MemoryContextAlloc(TopMemoryContext,
locallock->maxLockOwners * sizeof(LOCALLOCKOWNER)); locallock->maxLockOwners * sizeof(LOCALLOCKOWNER));
@ -994,8 +994,11 @@ LockAcquireExtended(const LOCKTAG *locktag,
static void static void
RemoveLocalLock(LOCALLOCK *locallock) RemoveLocalLock(LOCALLOCK *locallock)
{ {
pfree(locallock->lockOwners); locallock->numLockOwners = 0;
if (locallock->lockOwners != NULL)
pfree(locallock->lockOwners);
locallock->lockOwners = NULL; locallock->lockOwners = NULL;
if (!hash_search(LockMethodLocalHash, if (!hash_search(LockMethodLocalHash,
(void *) &(locallock->tag), (void *) &(locallock->tag),
HASH_REMOVE, NULL)) HASH_REMOVE, NULL))