Btrfs: remove BUG() in raid56

This BUG() has been triggered by a fuzz testing image, which contains
an invalid chunk type, ie. a single stripe chunk has the raid6 type.

Btrfs can handle this gracefully by returning -EIO, so besides using
btrfs_warn to give us more debugging information rather than a single
BUG(), we can return error properly.
Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/raid56.c

@@ -2143,7 +2143,10 @@ int raid56_parity_recover(struct btrfs_root *root, struct bio *bio,
 
 	rbio->faila = find_logical_bio_stripe(rbio, bio);
 	if (rbio->faila == -1) {
-		BUG();
+		btrfs_warn(root->fs_info,
+	"%s could not find the bad stripe in raid56 so that we cannot recover any more (bio has logical %llu len %llu, bbio has map_type %llu)",
+			   __func__, (u64)bio->bi_iter.bi_sector << 9,
+			   (u64)bio->bi_iter.bi_size, bbio->map_type);
 		if (generic_io)
 			btrfs_put_bbio(bbio);
 		kfree(rbio);