Re: [PATCH 1/2] btrfs: qgroup: Fix the wrong target io_tree when freeing reserved data space

[Nikolay Borisov <nborisov@suse.com>]

On 13.09.19 г. 4:51 ч., Qu Wenruo wrote:
> [BUG]
> Under the follow case with qgroup enabled, if some error happened after
> we have reserved delalloc space, then in error handling path, we could
> cause qgroup data space leakage:
> 
> From btrfs_truncate_block() in inode.c:
> 
> 	ret = btrfs_delalloc_reserve_space(inode, &data_reserved,
> 					   block_start, blocksize);
> 	if (ret)
> 		goto out;
> 
> again:
> 	page = find_or_create_page(mapping, index, mask);
> 	if (!page) {
> 		btrfs_delalloc_release_space(inode, data_reserved,
> 					     block_start, blocksize, true);
> 		btrfs_delalloc_release_extents(BTRFS_I(inode), blocksize, true);
> 		ret = -ENOMEM;
> 		goto out;
> 	}
> 
> [CAUSE]
> In above case, btrfs_delalloc_reserve_space() will call
> btrfs_qgroup_reserve_data() and mark the io_tree range with
> EXTENT_QGROUP_RESERVED flag.
> 
> In the error handling path, btrfs_delalloc_release_space() calls
> btrfs_qgroup_free_data() which should clear EXTENT_QGROUP_RESERVED flag
> and reduce the reserved data space accroding to the cleared range.
> 
> However due to a completion bug, btrfs_qgroup_free_data() will clear
> EXTENT_QGROUP_RESERVED flag in BTRFS_I(inode)->io_failure_tree, other
> than the correct BTRFS_I(inode)->io_tree.

This is a bit confusing because the error is actually in
qgroup_free_reserved_data, which is called from
__btrfs_qgroup_release_data. But in the latter function there is also a
call to clear_record_extent_bits with the correct tree. Just fix the
function name by using qgroup_free_reserved_data.

> Since io_failure_tree is never marked with that flag,
> btrfs_qgroup_free_data() will not free any data reserved space at all,
> causing a leakage.
> 
> All of such error handling cases can only be triggered some errors not

I take it you meant:

This error handling can only be triggered by errors outside of qgroup
e.g. EDQUOT can't triger the bug?

The first part of the sentence is hard to parse.

> from qgroup, so regular EDQUOT error won't trigger the bug.
> Normally we need error injection to trigger such bug.
> 
> [FIX]
> Fix the wrong target io_tree.
> 
> Reported-by: Josef Bacik <josef@toxicpanda.com>
> Fixes: bc42bda22345 ("btrfs: qgroup: Fix qgroup reserved space underflow by only freeing reserved ranges")
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>  fs/btrfs/qgroup.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
> index 2891b57b9e1e..64bdc3e3652d 100644
> --- a/fs/btrfs/qgroup.c
> +++ b/fs/btrfs/qgroup.c
> @@ -3492,7 +3492,7 @@ static int qgroup_free_reserved_data(struct inode *inode,
>  		 * EXTENT_QGROUP_RESERVED, we won't double free.
>  		 * So not need to rush.
>  		 */
> -		ret = clear_record_extent_bits(&BTRFS_I(inode)->io_failure_tree,
> +		ret = clear_record_extent_bits(&BTRFS_I(inode)->io_tree,
>  				free_start, free_start + free_len - 1,
>  				EXTENT_QGROUP_RESERVED, &changeset);
>  		if (ret < 0)
>