Tolerate partial pgstats entries in pgstat_gc_entry_refs()REL_16_STABLE

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 <ju.grigorev@ftdata.ru>
Discussion: https://postgr.es/m/aqtiKTvl519bu8-V@paquier.xyz
Backpatch-through: 15

0 files changed, 0 insertions, 0 deletions