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

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

On 2019/9/13 下午8:57, Nikolay Borisov wrote:
>
>
> 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.

Right, I ignored some caller here, as the caller chain is not only
dependent on btrfs_qgroup_free_data() but also on the parameter.
E.g. only when reserved is non-null we go 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?

Right.

I'll change it too something like "such leakage can only be triggered by
errors outside of qgroup."

Thanks,
Qu

>
> 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)
>>