Re: [PATCH] Fix SIGSEGV in GrantLockLocal when OOM leaves LOCALLOCK.lockOwners NULL

On Sat, Aug 08, 2026 at 10:26:40PM -0500, Bryan Green wrote:
> An out-of-memory error during the first LockAcquire for a lock tag leaves a
> LOCALLOCK that crashes the next acquire of the same tag.  The initial
> lockOwners allocation is done with maxLockOwners already set to 8 and
> lockOwners still NULL; if that allocation throws, the entry survives in that
> state.  The next acquire takes the existing-entry path, where the only check
> is numLockOwners >= maxLockOwners (0 >= 8, false), so it skips the
> allocation and GrantLockLocal() dereferences the NULL pointer.

else
{
/* Make sure there will be room to remember the lock */
- if (locallock->numLockOwners >= locallock->maxLockOwners)
+ if (locallock->lockOwners == NULL)
+ {
+ /* A prior acquisition left the array unallocated after OOM. */
+ locallock->maxLockOwners = 8;
+ locallock->lockOwners = (LOCALLOCKOWNER *)
+ MemoryContextAlloc(TopMemoryContext,
+ locallock->maxLockOwners * sizeof(LOCALLOCKOWNER));
+ }
+ else if (locallock->numLockOwners >= locallock->maxLockOwners)
{
int newsize = locallock->maxLockOwners * 2;

I can buy that. The allocation failing would leave lockOwners NULL
while there is an entry in LockMethodLocalHash that we may try to
re-access later. Just doing an extra allocation if we find out that
lockOwners is not set seems like a solution good enough.

Thanks for the report. Will look again at it later.
--
Michael