From fc29deb52106e710e9eba4d0f59ee185c8d200bf Mon Sep 17 00:00:00 2001 From: Michael Paquier Date: Thu, 17 Sep 2026 19:25:21 +0900 Subject: [PATCH] Tolerate partial pgstats entries in pgstat_gc_entry_refs() pgstat_get_entry_ref_cached() inserts a local entry_ref with shmem-related fields set to NULL, expecting pgstat_get_entry_ref() (its sole caller) to fill them up before returning. If an ERROR happens while pgstat_get_entry_ref() runs, it could be possible to finish with a local pgstats entry partially filled. This could lead to a crash of pgstat_gc_entry_refs(), which tolerates a NULL shared_stats in an assertion but unconditionally dereferenced its "dropped" and "generation" fields. This extends 4069df21beb8, being a cheap insurance against NULL pointer dereference, if some code paths of pgstat_get_entry_ref() are not able to perform any cleanup actions (for example after a dsm_create() throwing an ERROR). Reviewed-by: Grigorev Jurij Discussion: https://postgr.es/m/aqtiKTvl519bu8-V@paquier.xyz Backpatch-through: 15 --- src/backend/utils/activity/pgstat_shmem.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/src/backend/utils/activity/pgstat_shmem.c b/src/backend/utils/activity/pgstat_shmem.c index 58b99002f3f..7381afcd5c0 100644 --- a/src/backend/utils/activity/pgstat_shmem.c +++ b/src/backend/utils/activity/pgstat_shmem.c @@ -793,6 +793,15 @@ pgstat_gc_entry_refs(void) Assert(!entry_ref->shared_stats || entry_ref->shared_stats->magic == 0xdeadbeef); + /* A NULL shared_entry marks a partial reference. */ + if (entry_ref->shared_entry == NULL) + { + Assert(entry_ref->shared_stats == NULL); + Assert(entry_ref->pending == NULL); + pgstat_release_entry_ref(ent->key, entry_ref, false); + continue; + } + /* * "generation" checks for the case of entries being reinitialized, * and "dropped" for the case where these are.. dropped.