btrfs: handle failure of add_pending_csums

add_pending_csums was added as part of the new data=ordered
implementation in e6dcd2dc ("Btrfs: New data=ordered
implementation"). Even back then it called the btrfs_csum_file_blocks
which can fail but it never bothered handling the failure. In ENOMEM
situation this could lead to the filesystem failing to write the
checksums for a particular extent and not detect this. On read this
could lead to the filesystem erroring out due to crc mismatch. Fix it by
propagating failure from add_pending_csums and handling them.
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Josef Bacik <jbacik@fb.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/inode.c

@@ -2042,12 +2042,15 @@ static noinline int add_pending_csums(struct btrfs_trans_handle *trans,
 			     struct inode *inode, struct list_head *list)
 {
 	struct btrfs_ordered_sum *sum;
+	int ret;
 
 	list_for_each_entry(sum, list, list) {
 		trans->adding_csums = true;
-		btrfs_csum_file_blocks(trans,
+		ret = btrfs_csum_file_blocks(trans,
 		       BTRFS_I(inode)->root->fs_info->csum_root, sum);
 		trans->adding_csums = false;
+		if (ret)
+			return ret;
 	}
 	return 0;
 }
@@ -3061,7 +3064,11 @@ static int btrfs_finish_ordered_io(struct btrfs_ordered_extent *ordered_extent)
 		goto out;
 	}
 
-	add_pending_csums(trans, inode, &ordered_extent->list);
+	ret = add_pending_csums(trans, inode, &ordered_extent->list);
+	if (ret) {
+		btrfs_abort_transaction(trans, ret);
+		goto out;
+	}
 
 	btrfs_ordered_update_i_size(inode, 0, ordered_extent);
 	ret = btrfs_update_inode_fallback(trans, root, inode);