Fix race condition when sharing tuple descriptors.

macdice · macdice · commit b1d653890350 · 2021-05-29T15:12:34.000+12:00
Parallel query processes that called BlessTupleDesc() for identical tuple descriptors at the same moment could crash. There was code to handle that rare case, but it dereferenced a bogus DSA pointer. Repair. Back-patch to 11, where commit cc5f8136 added support for sharing tuple descriptors in parallel queries. Reported-by: Eric Thinnes <e.thinnes@gmx.de> Discussion: https://postgr.es/m/99aaa2eb-e194-bf07-c29a-1a76b4f2bcf9%40gmx.de
diff --git a/src/backend/utils/cache/typcache.c b/src/backend/utils/cache/typcache.c
@@ -2822,7 +2822,7 @@ find_or_make_matching_shared_tupledesc(TupleDesc tupdesc)
 		Assert(record_table_entry->key.shared);
 		result = (TupleDesc)
 			dsa_get_address(CurrentSession->area,
-							record_table_entry->key.shared);
+							record_table_entry->key.u.shared_tupdesc);
 		Assert(result->tdrefcount == -1);
 
 		return result;
