[XFS] Fix race in xfs_write() b/w dmapi callout and direct I/O checks.

In xfs_write() the iolock is dropped and reacquired in XFS_SEND_DATA()
which means that the file could change from not-cached to cached and we
need to redo the direct I/O checks. We should also redo the direct I/O
checks when the file size changes regardless if O_APPEND is set or not.

SGI-PV: 963483
SGI-Modid: xfs-linux-melb:xfs-kern:28440a

Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>

fs/xfs/linux-2.6/xfs_lrw.c

@@ -724,34 +724,8 @@ start:
 		goto out_unlock_mutex;
 	}
 
-	if (ioflags & IO_ISDIRECT) {
-		xfs_buftarg_t	*target =
-			(xip->i_d.di_flags & XFS_DIFLAG_REALTIME) ?
-				mp->m_rtdev_targp : mp->m_ddev_targp;
-
-		if ((pos & target->bt_smask) || (count & target->bt_smask)) {
-			xfs_iunlock(xip, XFS_ILOCK_EXCL|iolock);
-			return XFS_ERROR(-EINVAL);
-		}
-
-		if (!need_i_mutex && (VN_CACHED(vp) || pos > xip->i_size)) {
-			xfs_iunlock(xip, XFS_ILOCK_EXCL|iolock);
-			iolock = XFS_IOLOCK_EXCL;
-			locktype = VRWLOCK_WRITE;
-			need_i_mutex = 1;
-			mutex_lock(&inode->i_mutex);
-			xfs_ilock(xip, XFS_ILOCK_EXCL|iolock);
-			goto start;
-		}
-	}
-
-	new_size = pos + count;
-	if (new_size > xip->i_size)
-		io->io_new_size = new_size;
-
 	if ((DM_EVENT_ENABLED(vp->v_vfsp, xip, DM_EVENT_WRITE) &&
 	    !(ioflags & IO_INVIS) && !eventsent)) {
-		loff_t		savedsize = pos;
 		int		dmflags = FILP_DELAY_FLAG(file);
 
 		if (need_i_mutex)
@@ -774,10 +748,35 @@ start:
 		 * event prevents another call to XFS_SEND_DATA, which is
 		 * what allows the size to change in the first place.
 		 */
-		if ((file->f_flags & O_APPEND) && savedsize != xip->i_size)
+		if ((file->f_flags & O_APPEND) && pos != xip->i_size)
 			goto start;
 	}
 
+	if (ioflags & IO_ISDIRECT) {
+		xfs_buftarg_t	*target =
+			(xip->i_d.di_flags & XFS_DIFLAG_REALTIME) ?
+				mp->m_rtdev_targp : mp->m_ddev_targp;
+
+		if ((pos & target->bt_smask) || (count & target->bt_smask)) {
+			xfs_iunlock(xip, XFS_ILOCK_EXCL|iolock);
+			return XFS_ERROR(-EINVAL);
+		}
+
+		if (!need_i_mutex && (VN_CACHED(vp) || pos > xip->i_size)) {
+			xfs_iunlock(xip, XFS_ILOCK_EXCL|iolock);
+			iolock = XFS_IOLOCK_EXCL;
+			locktype = VRWLOCK_WRITE;
+			need_i_mutex = 1;
+			mutex_lock(&inode->i_mutex);
+			xfs_ilock(xip, XFS_ILOCK_EXCL|iolock);
+			goto start;
+		}
+	}
+
+	new_size = pos + count;
+	if (new_size > xip->i_size)
+		io->io_new_size = new_size;
+
 	if (likely(!(ioflags & IO_INVIS))) {
 		file_update_time(file);
 		xfs_ichgtime_fast(xip, inode,