[XFS] Fix double free of log tickets

When an I/O error occurs during an intermediate commit on a rolling
transaction, xfs_trans_commit() will free the transaction structure
and the related ticket. However, the duplicate transaction that
gets used as the transaction continues still contains a pointer
to the ticket. Hence when the duplicate transaction is cancelled
and freed, we free the ticket a second time.

Add reference counting to the ticket so that we hold an extra
reference to the ticket over the transaction commit. We drop the
extra reference once we have checked that the transaction commit
did not return an error, thus avoiding a double free on commit
error.

Credit to Nick Piggin for tripping over the problem.

SGI-PV: 989741

Signed-off-by: Dave Chinner <david@fromorbit.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>

1 files changed, 25 insertions, 14 deletions

diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index 92c20a8..4bf44ae 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -100,12 +100,11 @@ STATIC void xlog_ungrant_log_space(xlog_t	 *log,
 
 
 /* local ticket functions */
-STATIC xlog_ticket_t	*xlog_ticket_get(xlog_t *log,
+STATIC xlog_ticket_t	*xlog_ticket_alloc(xlog_t *log,
 					 int	unit_bytes,
 					 int	count,
 					 char	clientid,
 					 uint	flags);
-STATIC void		xlog_ticket_put(xlog_t *log, xlog_ticket_t *ticket);
 
 #if defined(DEBUG)
 STATIC void	xlog_verify_dest_ptr(xlog_t *log, __psint_t ptr);
@@ -360,7 +359,7 @@ xfs_log_done(xfs_mount_t	*mp,
 		 */
 		xlog_trace_loggrant(log, ticket, "xfs_log_done: (non-permanent)");
 		xlog_ungrant_log_space(log, ticket);
-		xlog_ticket_put(log, ticket);
+		xfs_log_ticket_put(ticket);
 	} else {
 		xlog_trace_loggrant(log, ticket, "xfs_log_done: (permanent)");
 		xlog_regrant_reserve_log_space(log, ticket);
@@ -514,7 +513,7 @@ xfs_log_reserve(xfs_mount_t	 *mp,
 		retval = xlog_regrant_write_log_space(log, internal_ticket);
 	} else {
 		/* may sleep if need to allocate more tickets */
-		internal_ticket = xlog_ticket_get(log, unit_bytes, cnt,
+		internal_ticket = xlog_ticket_alloc(log, unit_bytes, cnt,
 						  client, flags);
 		if (!internal_ticket)
 			return XFS_ERROR(ENOMEM);
@@ -749,7 +748,7 @@ xfs_log_unmount_write(xfs_mount_t *mp)
 		if (tic) {
 			xlog_trace_loggrant(log, tic, "unmount rec");
 			xlog_ungrant_log_space(log, tic);
-			xlog_ticket_put(log, tic);
+			xfs_log_ticket_put(tic);
 		}
 	} else {
 		/*
@@ -3222,22 +3221,33 @@ xlog_state_want_sync(xlog_t *log, xlog_in_core_t *iclog)
  */
 
 /*
- * Free a used ticket.
+ * Free a used ticket when it's refcount falls to zero.
  */
-STATIC void
-xlog_ticket_put(xlog_t		*log,
-		xlog_ticket_t	*ticket)
+void
+xfs_log_ticket_put(
+	xlog_ticket_t	*ticket)
 {
-	sv_destroy(&ticket->t_wait);
-	kmem_zone_free(xfs_log_ticket_zone, ticket);
-}	/* xlog_ticket_put */
+	ASSERT(atomic_read(&ticket->t_ref) > 0);
+	if (atomic_dec_and_test(&ticket->t_ref)) {
+		sv_destroy(&ticket->t_wait);
+		kmem_zone_free(xfs_log_ticket_zone, ticket);
+	}
+}
 
+xlog_ticket_t *
+xfs_log_ticket_get(
+	xlog_ticket_t	*ticket)
+{
+	ASSERT(atomic_read(&ticket->t_ref) > 0);
+	atomic_inc(&ticket->t_ref);
+	return ticket;
+}
 
 /*
  * Allocate and initialise a new log ticket.
  */
 STATIC xlog_ticket_t *
-xlog_ticket_get(xlog_t		*log,
+xlog_ticket_alloc(xlog_t		*log,
 		int		unit_bytes,
 		int		cnt,
 		char		client,
@@ -3308,6 +3318,7 @@ xlog_ticket_get(xlog_t		*log,
 		unit_bytes += 2*BBSIZE;
         }
 
+	atomic_set(&tic->t_ref, 1);
 	tic->t_unit_res		= unit_bytes;
 	tic->t_curr_res		= unit_bytes;
 	tic->t_cnt		= cnt;
@@ -3323,7 +3334,7 @@ xlog_ticket_get(xlog_t		*log,
 	xlog_tic_reset_res(tic);
 
 	return tic;
-}	/* xlog_ticket_get */
+}
 
 
 /******************************************************************************