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Tolerate partial pgstats entries in pgstat_gc_entry_refs()

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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 4069df21be, 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 <ju.grigorev@ftdata.ru>
Discussion: https://postgr.es/m/aqtiKTvl519bu8-V@paquier.xyz
Backpatch-through: 15
This commit is contained in:
Michael Paquier
2026-09-17 19:25:32 +09:00
parent 11545bba7f
commit 0016a2cc4f
1 changed files with 9 additions and 0 deletions
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9
src/backend/utils/activity/pgstat_shmem.c
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@@ -738,6 +738,15 @@ 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.