ext4: add shutdown bit and check for it

Add a shutdown bit that will cause ext4 processing to fail immediately
with EIO.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index d83b0f3..f880883 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -158,7 +158,7 @@ static int ext4_end_io(ext4_io_end_t *io)
 
 	io->handle = NULL;	/* Following call will use up the handle */
 	ret = ext4_convert_unwritten_extents(handle, inode, offset, size);
-	if (ret < 0) {
+	if (ret < 0 && !ext4_forced_shutdown(EXT4_SB(inode->i_sb))) {
 		ext4_msg(inode->i_sb, KERN_EMERG,
 			 "failed to convert unwritten extents to written "
 			 "extents -- potential data loss!  "