postgres.git / summary / log / commit / refs

commit    03a37e9bba2f2bd8ce53cec4efc32ed5c3e38dc7
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Mon Jan 26 16:57:44 2015 +0000

    Fix volatile-safety issue in asyncQueueReadAllNotifications().
    
    The "pos" variable is modified within PG_TRY and then referenced
    within PG_CATCH, so for strict POSIX conformance it must be marked
    volatile.  Superficially the code looked safe because pos's address
    was taken, which was sufficient to force it into memory ... but it's
    not sufficient to ensure that the compiler applies updates exactly
    where the program text says to.  The volatility marking has to extend
    into a couple of subroutines too, but I think that's probably a good
    thing because the risk of out-of-order updates is mostly in those
    subroutines not asyncQueueReadAllNotifications() itself.  In principle
    the compiler could have re-ordered operations such that an error could
    be thrown while "pos" had an incorrect value.
    
    It's unclear how real the risk is here, but for safety back-patch
    to all active branches.


 src/backend/commands/async.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/backend/commands/async.c b/src/backend/commands/async.c
index bc85ed73f5c..6fc9313e8f0 100644
--- a/src/backend/commands/async.c
+++ b/src/backend/commands/async.c
@@ -371,13 +371,13 @@ static void Exec_UnlistenAllCommit(void);
 static bool IsListeningOn(const char *channel);
 static void asyncQueueUnregister(void);
 static bool asyncQueueIsFull(void);
-static bool asyncQueueAdvance(QueuePosition *position, int entryLength);
+static bool asyncQueueAdvance(volatile QueuePosition *position, int entryLength);
 static void asyncQueueNotificationToEntry(Notification *n, AsyncQueueEntry *qe);
 static ListCell *asyncQueueAddEntries(ListCell *nextNotify);
 static void asyncQueueFillWarning(void);
 static bool SignalBackends(void);
 static void asyncQueueReadAllNotifications(void);
-static bool asyncQueueProcessPageEntries(QueuePosition *current,
+static bool asyncQueueProcessPageEntries(volatile QueuePosition *current,
 							 QueuePosition stop,
 							 char *page_buffer);
 static void asyncQueueAdvanceTail(void);
@@ -1225,7 +1225,7 @@ asyncQueueIsFull(void)
  * returns true, else false.
  */
 static bool
-asyncQueueAdvance(QueuePosition *position, int entryLength)
+asyncQueueAdvance(volatile QueuePosition *position, int entryLength)
 {
 	int			pageno = QUEUE_POS_PAGE(*position);
 	int			offset = QUEUE_POS_OFFSET(*position);
@@ -1815,7 +1815,7 @@ DisableNotifyInterrupt(void)
 static void
 asyncQueueReadAllNotifications(void)
 {
-	QueuePosition pos;
+	volatile QueuePosition pos;
 	QueuePosition oldpos;
 	QueuePosition head;
 	bool		advanceTail;
@@ -1975,7 +1975,7 @@ asyncQueueReadAllNotifications(void)
  * The QueuePosition *current is advanced past all processed messages.
  */
 static bool
-asyncQueueProcessPageEntries(QueuePosition *current,
+asyncQueueProcessPageEntries(volatile QueuePosition *current,
 							 QueuePosition stop,
 							 char *page_buffer)
 {


[parent: b00a0885918f]