Fix unsafe coding in ReorderBufferCommit().

tglsfdc · tglsfdc · commit 91964c3ed1c4 · 2015-01-24T13:25:22.000-05:00
"iterstate" must be marked volatile since it's changed inside the PG_TRY
block and then used in the PG_CATCH stanza.  Noted by Mark Wilding of
Salesforce.  (We really need to see if we can't get the C compiler to warn
about this.)

Also, reset iterstate to NULL after the mainline ReorderBufferIterTXNFinish
call, to ensure the PG_CATCH block doesn't try to do that a second time.
diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
@@ -1259,7 +1259,7 @@ ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,
 					TimestampTz commit_time)
 {
 	ReorderBufferTXN *txn;
-	ReorderBufferIterTXNState *iterstate = NULL;
+	ReorderBufferIterTXNState *volatile iterstate = NULL;
 	ReorderBufferChange *change;
 
 	volatile CommandId command_id = FirstCommandId;
@@ -1304,7 +1304,6 @@ ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,
 
 	PG_TRY();
 	{
-
 		/*
 		 * Decoding needs access to syscaches et al., which in turn use
 		 * heavyweight locks and such. Thus we need to have enough state
@@ -1473,7 +1472,9 @@ ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,
 			}
 		}
 
+		/* clean up the iterator */
 		ReorderBufferIterTXNFinish(rb, iterstate);
+		iterstate = NULL;
 
 		/* call commit callback */
 		rb->commit(rb, txn, commit_lsn);
@@ -1640,7 +1641,7 @@ ReorderBufferForget(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn)
 	 */
 	if (txn->base_snapshot != NULL && txn->ninvalidations > 0)
 	{
-		bool use_subtxn = IsTransactionOrTransactionBlock();
+		bool		use_subtxn = IsTransactionOrTransactionBlock();
 
 		if (use_subtxn)
 			BeginInternalSubTransaction("replay");

Original file line number	Diff line number	Diff line change
`@@ -1259,7 +1259,7 @@ ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,`
`1259`	`1259`	`TimestampTz commit_time)`
`1260`	`1260`	`{`
`1261`	`1261`	`ReorderBufferTXN *txn;`
`1262`		`- ReorderBufferIterTXNState *iterstate = NULL;`
	`1262`	`+ ReorderBufferIterTXNState *volatile iterstate = NULL;`
`1263`	`1263`	`ReorderBufferChange *change;`
`1264`	`1264`
`1265`	`1265`	`volatile CommandId command_id = FirstCommandId;`
`@@ -1304,7 +1304,6 @@ ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,`
`1304`	`1304`
`1305`	`1305`	`PG_TRY();`
`1306`	`1306`	`{`
`1307`		`-`
`1308`	`1307`	`/*`
`1309`	`1308`	`* Decoding needs access to syscaches et al., which in turn use`
`1310`	`1309`	`* heavyweight locks and such. Thus we need to have enough state`
`@@ -1473,7 +1472,9 @@ ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,`
`1473`	`1472`	`}`
`1474`	`1473`	`}`
`1475`	`1474`
	`1475`	`+ /* clean up the iterator */`
`1476`	`1476`	`ReorderBufferIterTXNFinish(rb, iterstate);`
	`1477`	`+ iterstate = NULL;`
`1477`	`1478`
`1478`	`1479`	`/* call commit callback */`
`1479`	`1480`	`rb->commit(rb, txn, commit_lsn);`
`@@ -1640,7 +1641,7 @@ ReorderBufferForget(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn)`
`1640`	`1641`	`*/`
`1641`	`1642`	`if (txn->base_snapshot != NULL && txn->ninvalidations > 0)`
`1642`	`1643`	`{`
`1643`		`- bool use_subtxn = IsTransactionOrTransactionBlock();`
	`1644`	`+ bool use_subtxn = IsTransactionOrTransactionBlock();`
`1644`	`1645`
`1645`	`1646`	`if (use_subtxn)`
`1646`	`1647`	`BeginInternalSubTransaction("replay");`