Re: race condition in pg_class

On Mon, Oct 21, 2024 at 10:00:00PM +0300, Alexander Lakhin wrote:
> Please look at an anomaly introduced with a07e03fd8.
> With the attached modification for intra-grant-inplace.spec, running this
> test triggers a Valgrind-detected error for me:
> ==00:00:00:09.624 319033== Conditional jump or move depends on uninitialised value(s)
> ==00:00:00:09.624 319033==    at 0x25D120: DoesMultiXactIdConflict (heapam.c:7373)
> ==00:00:00:09.624 319033==    by 0x25B45A: heap_inplace_lock (heapam.c:6265)
> ==00:00:00:09.624 319033==    by 0x27D8CB: systable_inplace_update_begin (genam.c:867)
> ==00:00:00:09.624 319033==    by 0x33F717: index_update_stats (index.c:2856)
> ==00:00:00:09.624 319033==    by 0x33FEE2: index_build (index.c:3106)
> ==00:00:00:09.625 319033==    by 0x33C7D3: index_create (index.c:1276)
> ==00:00:00:09.625 319033==    by 0x451000: DefineIndex (indexcmds.c:1216)
> ==00:00:00:09.625 319033==    by 0x48D091: ATExecAddIndex (tablecmds.c:9156)
> ==00:00:00:09.625 319033==    by 0x483F8E: ATExecCmd (tablecmds.c:5302)
> ==00:00:00:09.625 319033==    by 0x483877: ATRewriteCatalogs (tablecmds.c:5186)
> ==00:00:00:09.625 319033==    by 0x482B9A: ATController (tablecmds.c:4741)
> ==00:00:00:09.625 319033==    by 0x4827A1: AlterTable (tablecmds.c:4387)
> ==00:00:00:09.625 319033==

Thanks.

> Perhaps current_is_member in heap_inplace_lock() should be initialized
> before the DoesMultiXactIdConflict() call as in other places...

heap_inplace_lock() ignores current_is_member after computing it, so let's
just pass NULL, as attached.