Unset MyBEEntry, making elog.c's call to pgstat_get_my_query_id() safe.

anarazel · anarazel · commit bed5eac2d50e · 2021-08-19T05:07:53.000-07:00
Previously log messages late during shutdown could end up using either another backend's PgBackendStatus (multi user) or segfault (single user) because pgstat_get_my_query_id()'s check for !MyBEEntry didn't filter out use after pgstat_beshutdown_hook(). This became a bug in 4f0b096, but was a bit fishy before. But given there's no known problematic cases before 14, it doesn't seem worth backpatching further. Also fixes a wrong filename in a comment, introduced in e102504. Reported-By: Andres Freund <andres@anarazel.de> Reviewed-By: Julien Rouhaud <rjuju123@gmail.com> Discussion: https://postgr.es/m/Julien Rouhaud <rjuju123@gmail.com> Backpatch: 14-
diff --git a/src/backend/utils/activity/backend_status.c b/src/backend/utils/activity/backend_status.c
@@ -46,7 +46,7 @@ bool		pgstat_track_activities = false;
 int			pgstat_track_activity_query_size = 1024;
 
 
-/* exposed so that progress.c can access it */
+/* exposed so that backend_progress.c can access it */
 PgBackendStatus *MyBEEntry = NULL;
 
 
@@ -469,6 +469,9 @@ pgstat_beshutdown_hook(int code, Datum arg)
 	beentry->st_procpid = 0;	/* mark invalid */
 
 	PGSTAT_END_WRITE_ACTIVITY(beentry);
+
+	/* so that functions can check if backend_status.c is up via MyBEEntry */
+	MyBEEntry = NULL;
 }
 
 /*
