[XFS] Warn on transaction in flight on read-only remount

Till VFS can correctly support read-only remount without racing,
use WARN_ON instead of BUG_ON on detecting transaction in flight
after quiescing filesystem.

Signed-off-by: Felix Blyakher <felixb@sgi.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/linux-2.6/xfs_sync.c

@@ -371,7 +371,11 @@ xfs_quiesce_attr(
 	/* flush inodes and push all remaining buffers out to disk */
 	xfs_quiesce_fs(mp);
 
-	ASSERT_ALWAYS(atomic_read(&mp->m_active_trans) == 0);
+	/*
+	 * Just warn here till VFS can correctly support
+	 * read-only remount without racing.
+	 */
+	WARN_ON(atomic_read(&mp->m_active_trans) != 0);
 
 	/* Push the superblock and write an unmount record */
 	error = xfs_log_sbcount(mp, 1);