btrfs: adjust dirty_metadata_bytes after writeback failure of extent buffer

Before, if a eb failed to write out, we would end up triggering a
BUG_ON(). As of f4340622 ("btrfs: extent_io: Move the BUG_ON() in
flush_write_bio() one level up"), we no longer BUG_ON(), so we should
make life consistent and add back the unwritten bytes to
dirty_metadata_bytes.

Fixes: f4340622 ("btrfs: extent_io: Move the BUG_ON() in flush_write_bio() one level up")
CC: stable@vger.kernel.org # 5.2+
Reviewed-by: Filipe Manana <fdmanana@kernel.org>
Signed-off-by: Dennis Zhou <dennis@kernel.org>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -3728,11 +3728,20 @@ static void end_extent_buffer_writeback(struct extent_buffer *eb)
 static void set_btree_ioerr(struct page *page)
 {
 	struct extent_buffer *eb = (struct extent_buffer *)page->private;
+	struct btrfs_fs_info *fs_info;
 
 	SetPageError(page);
 	if (test_and_set_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags))
 		return;
 
+	/*
+	 * If we error out, we should add back the dirty_metadata_bytes
+	 * to make it consistent.
+	 */
+	fs_info = eb->fs_info;
+	percpu_counter_add_batch(&fs_info->dirty_metadata_bytes,
+				 eb->len, fs_info->dirty_metadata_batch);
+
 	/*
 	 * If writeback for a btree extent that doesn't belong to a log tree
 	 * failed, increment the counter transaction->eb_write_errors.