Btrfs: bail out gracefully rather than BUG_ON

If a file's DIR_ITEM key is invalid (due to memory errors) and gets
written to disk, a future lookup_path can end up with kernel panic due
to BUG_ON().

This gets rid of the BUG_ON(), meanwhile output the corrupted key and
return ENOENT if it's invalid.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reported-by: Guillaume Bouchard <bouchard@mercs-eng.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/inode.c

@@ -5445,6 +5445,14 @@ static int btrfs_inode_by_name(struct inode *dir, struct dentry *dentry,
 		goto out_err;
 
 	btrfs_dir_item_key_to_cpu(path->nodes[0], di, location);
+	if (location->type != BTRFS_INODE_ITEM_KEY &&
+	    location->type != BTRFS_ROOT_ITEM_KEY) {
+		btrfs_warn(root->fs_info,
+"%s gets something invalid in DIR_ITEM (name %s, directory ino %llu, location(%llu %u %llu))",
+			   __func__, name, btrfs_ino(BTRFS_I(dir)),
+			   location->objectid, location->type, location->offset);
+		goto out_err;
+	}
 out:
 	btrfs_free_path(path);
 	return ret;
@@ -5761,8 +5769,6 @@ struct inode *btrfs_lookup_dentry(struct inode *dir, struct dentry *dentry)
 		return inode;
 	}
 
-	BUG_ON(location.type != BTRFS_ROOT_ITEM_KEY);
-
 	index = srcu_read_lock(&fs_info->subvol_srcu);
 	ret = fixup_tree_root_location(fs_info, dir, dentry,
 				       &location, &sub_root);