ext2: clear uptodate flag on super block I/O error

This fixes a WARN backtrace in mark_buffer_dirty() that occurs during
unmount when a USB or floppy device is removed. I reported this a kernel
regression, but looks like it might have been there for longer
than that.

The super block update from a previous operation has marked the buffer
as in error, and the flag has to be cleared before doing the update.
(Similar code already exists in ext4).
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/ext2/super.c

@@ -1137,8 +1137,24 @@ static void ext2_sync_super(struct super_block *sb, struct ext2_super_block *es)
 static int ext2_sync_fs(struct super_block *sb, int wait)
 {
 	struct ext2_super_block *es = EXT2_SB(sb)->s_es;
+	struct buffer_head *sbh = EXT2_SB(sb)->s_sbh;
 
 	lock_kernel();
+	if (buffer_write_io_error(sbh)) {
+		/*
+		 * Oh, dear.  A previous attempt to write the
+		 * superblock failed.  This could happen because the
+		 * USB device was yanked out.  Or it could happen to
+		 * be a transient write error and maybe the block will
+		 * be remapped.  Nothing we can do but to retry the
+		 * write and hope for the best.
+		 */
+		ext2_msg(sb, KERN_ERR,
+		       "previous I/O error to superblock detected\n");
+		clear_buffer_write_io_error(sbh);
+		set_buffer_uptodate(sbh);
+	}
+
 	if (es->s_state & cpu_to_le16(EXT2_VALID_FS)) {
 		ext2_debug("setting valid to 0\n");
 		es->s_state &= cpu_to_le16(~EXT2_VALID_FS);