Fix the initialization of atomic variable introduced by the

Amit Kapila · Amit Kapila · commit 1a8bde490c98 · 2018-11-13T10:43:35.000+05:30
group clearing mechanism. Commit 0e141c0 introduced initialization of atomic variable in InitProcess which means that it's not safe to look at it for backends that aren't currently in use. Fix that by initializing the same during postmaster startup. Reported-by: Andres Freund Author: Amit Kapila Backpatch-through: 9.6 Discussion: https://postgr.es/m/20181027104138.qmbbelopvy7cw2qv@alap3.anarazel.de
diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c
@@ -268,6 +268,12 @@ InitProcGlobal(void)
 
 		/* Initialize lockGroupMembers list. */
 		dlist_init(&procs[i].lockGroupMembers);
+
+		/*
+		 * Initialize the atomic variable, otherwise, it won't be safe to
+		 * access it for backends that aren't currently in use.
+		 */
+		pg_atomic_init_u32(&(procs[i].procArrayGroupNext), INVALID_PGPROCNO);
 	}
 
 	/*
@@ -401,7 +407,7 @@ InitProcess(void)
 	/* Initialize fields for group XID clearing. */
 	MyProc->procArrayGroupMember = false;
 	MyProc->procArrayGroupMemberXid = InvalidTransactionId;
-	pg_atomic_init_u32(&MyProc->procArrayGroupNext, INVALID_PGPROCNO);
+	Assert(pg_atomic_read_u32(&MyProc->procArrayGroupNext) == INVALID_PGPROCNO);
 
 	/* Check that group locking fields are in a proper initial state. */
 	Assert(MyProc->lockGroupLeader == NULL);
