Fix the initialization of atomic variables introduced by the

Amit Kapila · Amit Kapila · commit a53bc135fb07 · 2018-11-13T10:52:40.000+05:30
group clearing mechanism. Commits 0e141c0 and baaf272 introduced initialization of atomic variables in InitProcess which means that it's not safe to look at those for backends that aren't currently in use. Fix that by initializing them 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
@@ -267,6 +267,13 @@ InitProcGlobal(void)
 
 		/* Initialize lockGroupMembers list. */
 		dlist_init(&procs[i].lockGroupMembers);
+
+		/*
+		 * Initialize the atomic variables, otherwise, it won't be safe to
+		 * access them for backends that aren't currently in use.
+		 */
+		pg_atomic_init_u32(&(procs[i].procArrayGroupNext), INVALID_PGPROCNO);
+		pg_atomic_init_u32(&(procs[i].clogGroupNext), INVALID_PGPROCNO);
 	}
 
 	/*
@@ -401,7 +408,7 @@ 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);
@@ -416,7 +423,7 @@ InitProcess(void)
 	MyProc->clogGroupMemberXidStatus = TRANSACTION_STATUS_IN_PROGRESS;
 	MyProc->clogGroupMemberPage = -1;
 	MyProc->clogGroupMemberLsn = InvalidXLogRecPtr;
-	pg_atomic_init_u32(&MyProc->clogGroupNext, INVALID_PGPROCNO);
+	Assert(pg_atomic_read_u32(&MyProc->clogGroupNext) == INVALID_PGPROCNO);
 
 	/*
 	 * Acquire ownership of the PGPROC's latch, so that we can use WaitLatch
