Re: [PATCH 2/2] Btrfs: report and handle error on unexpected first key on extent buffer

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

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On 2019/2/19 上午12:58, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> When there is a kind of corruption in an extent buffer such that its first
> key does not match the key at the respective parent slot, one of two things
> happens:

Isn't that handled by read_tree_block() already?

Thanks,
Qu

> 
> 1) When assertions are enabled, we effectively hit a BUG_ON() which
>    requires rebooting the machine later. This also does not tell any
>    information about which extent buffer is affected, from which root,
>    the expected and found keys, etc.
> 
> 2) When assertions are disabled, we just ignore the mismatch and assume
>    everything is ok, which can potentially lead to all sorts of unexpected
>    problems later after a tree search (in the worst case, could lead to
>    further silent corruption).
> 
> So improve this by always checking if the first key of an extent buffer is
> what it's supposed to be, when doing a key search at key_search(), and
> report and return an appropriate error. The overhead is just comparing one
> key, which is minimal and is anyway just done in a special case where we
> skip the more expensive binary search (the binary search in the parent
> node returned 0, exact key match).
> 
> Signed-off-by: Filipe Manana <fdmanana@suse.com>
> ---
>  fs/btrfs/ctree.c | 38 +++++++++++++++++---------------------
>  1 file changed, 17 insertions(+), 21 deletions(-)
> 
> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
> index 5b9f602fb9e2..a0bd0278208d 100644
> --- a/fs/btrfs/ctree.c
> +++ b/fs/btrfs/ctree.c
> @@ -2529,35 +2529,31 @@ setup_nodes_for_search(struct btrfs_trans_handle *trans,
>  	return ret;
>  }
>  
> -static void key_search_validate(struct extent_buffer *b,
> -				const struct btrfs_key *key,
> -				int level)
> -{
> -#ifdef CONFIG_BTRFS_ASSERT
> -	struct btrfs_disk_key disk_key;
> -
> -	btrfs_cpu_key_to_disk(&disk_key, key);
> -
> -	if (level == 0)
> -		ASSERT(!memcmp_extent_buffer(b, &disk_key,
> -		    offsetof(struct btrfs_leaf, items[0].key),
> -		    sizeof(disk_key)));
> -	else
> -		ASSERT(!memcmp_extent_buffer(b, &disk_key,
> -		    offsetof(struct btrfs_node, ptrs[0].key),
> -		    sizeof(disk_key)));
> -#endif
> -}
> -
>  static int key_search(struct extent_buffer *b, const struct btrfs_key *key,
>  		      int level, int *prev_cmp, int *slot)
>  {
> +	struct btrfs_key found_key;
> +
>  	if (*prev_cmp != 0) {
>  		*prev_cmp = btrfs_bin_search(b, key, level, slot);
>  		return *prev_cmp;
>  	}
>  
> -	key_search_validate(b, key, level);
> +	if (level == 0)
> +		btrfs_item_key_to_cpu(b, &found_key, 0);
> +	else
> +		btrfs_node_key_to_cpu(b, &found_key, 0);
> +
> +	if (btrfs_comp_cpu_keys(&found_key, key) != 0) {
> +		btrfs_crit(b->fs_info,
> +"unexpected first key for extent buffer: bytenr=%llu level=%d root=%llu expected key=(%llu %u %llu) found key=(%llu %u %llu)",
> +			   btrfs_header_bytenr(b), level, btrfs_header_owner(b),
> +			   key->objectid, key->type, key->offset,
> +			   found_key.objectid, found_key.type,
> +			   found_key.offset);
> +		return -EUCLEAN;
> +	}
> +
>  	*slot = 0;
>  
>  	return 0;
> 


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