Re: [PATCH 07/20] btrfs: handle chunk tree lookup error in btrfs_relocate_sys_chunks()

From: Qu Wenruo <quwenruo.btrfs@gmx.com>
To: David Sterba <dsterba@suse.com>, linux-btrfs@vger.kernel.org
Subject: Re: [PATCH 07/20] btrfs: handle chunk tree lookup error in btrfs_relocate_sys_chunks()
Date: Thu, 25 Jan 2024 14:38:17 +1030	[thread overview]
Message-ID: <21add1cf-d22e-4a95-a293-65ac51b7ec23@gmx.com> (raw)
In-Reply-To: <ae9556ccc1c06b17ea40f2e05b60cc4d8dcac0a7.1706130791.git.dsterba@suse.com>

On 2024/1/25 07:48, David Sterba wrote:
> The unhandled case in btrfs_relocate_sys_chunks() loop is a corruption,
> as it could be caused only by two impossible conditions:
>
> - at first the search key is set up to look for a chunk tree item, with
>    offset -1, this is an inexact search and the key->offset will contain
>    the correct offset upon a successful search, a valid chunk tree item
>    cannot have an offset -1
>
> - after first successful search, the found_key corresponds to a chunk
>    item, the offset is decremented by 1 before the next loop, it's
>    impossible to find a chunk item there due to alignment and size
>    constraints
>
> Signed-off-by: David Sterba <dsterba@suse.com>
> ---
>   fs/btrfs/volumes.c | 12 +++++++++++-
>   1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index d67785be2c77..6aae92e4b424 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -3393,7 +3393,17 @@ static int btrfs_relocate_sys_chunks(struct btrfs_fs_info *fs_info)
>   			mutex_unlock(&fs_info->reclaim_bgs_lock);
>   			goto error;
>   		}
> -		BUG_ON(ret == 0); /* Corruption */
> +		if (ret == 0) {
> +			/*
> +			 * On the first search we would find chunk tree with
> +			 * offset -1, which is not possible. On subsequent
> +			 * loops this would find an existing item on an invalid
> +			 * offset (one less than the previous one, wrong
> +			 * alignment and size).
> +			 */
> +			ret = -EUCLEAN;
> +			goto error;

This can be handled by adding new root item offset key check in
tree-checker, then converting to an ASSERT().

Thanks,
Qu
> +		}
>
>   		ret = btrfs_previous_item(chunk_root, path, key.objectid,
>   					  key.type);