postgres.git / summary / log / commit / refs

commit    16706f1f4dc202d502f07f7b14bb600eb0daef92
Author:   Michael Paquier <michael@paquier.xyz>
Date:     Thu Sep 17 10:25:12 2026 +0000

    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 <ju.grigorev@ftdata.ru>
    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 d8ac9d6f5e8..5feed5f842a 100644
--- a/src/backend/utils/activity/pgstat_shmem.c
+++ b/src/backend/utils/activity/pgstat_shmem.c
@@ -828,6 +828,15 @@ 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.