btrfs: do proper error handling in record_reloc_root_in_trans

Generally speaking this shouldn't ever fail, the corresponding fs root
for the reloc root will already be in memory, so we won't get ENOMEM
here.

However if there is no corresponding root for the reloc root then we
could get ENOMEM when we try to allocate it or we could get ENOENT
when we look it up and see that it doesn't exist.

Convert these BUG_ON()'s into ASSERT()'s and add proper error handling
for the case of corruption.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/relocation.c

@@ -1971,8 +1971,27 @@ static int record_reloc_root_in_trans(struct btrfs_trans_handle *trans,
 		return 0;
 
 	root = btrfs_get_fs_root(fs_info, reloc_root->root_key.offset, false);
-	BUG_ON(IS_ERR(root));
-	BUG_ON(root->reloc_root != reloc_root);
+
+	/*
+	 * This should succeed, since we can't have a reloc root without having
+	 * already looked up the actual root and created the reloc root for this
+	 * root.
+	 *
+	 * However if there's some sort of corruption where we have a ref to a
+	 * reloc root without a corresponding root this could return ENOENT.
+	 */
+	if (IS_ERR(root)) {
+		ASSERT(0);
+		return PTR_ERR(root);
+	}
+	if (root->reloc_root != reloc_root) {
+		ASSERT(0);
+		btrfs_err(fs_info,
+			  "root %llu has two reloc roots associated with it",
+			  reloc_root->root_key.offset);
+		btrfs_put_root(root);
+		return -EUCLEAN;
+	}
 	ret = btrfs_record_root_in_trans(trans, root);
 	btrfs_put_root(root);