On 24.10.2017 15:19, Qu Wenruo wrote:
>
>
> On 2017年10月24日 20:01, Nikolay Borisov wrote:
>>
>>
>> On 24.10.2017 11:39, Qu Wenruo wrote:
>>> When modifying qgroup relationship, for qgroup which only owns exclusive
>>> extents, we will go through quick update path.
>>>
>>> In quick update path, we will just adding/removing exclusive and reference
>>> number.
>>>
>>> However we did the opposite for qgroup reservation from the very
>>> beginning.
>>
>> I'm afraid this sentence doesn't give much information about what's
>> really going on.
>
> I'll try to reorganize it to give a better explanation on this.
>
>>
>>>
>>> In fact, we should also inherit the qgroup reservation space, just like
>>> exclusive and reference numbers.
>>>
>>> Fix by using the newly introduced
>>> qgroup_rsv_increase/decrease_by_qgroup() function call.
>>>
>>> Signed-off-by: Qu Wenruo <w...@suse.com>
>>> ---
>>> fs/btrfs/qgroup.c | 39 ++++++++++++++++++---------------------
>>> 1 file changed, 18 insertions(+), 21 deletions(-)
>>>
>>> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
>>> index 7b89da9589c1..ba6f60fd0e96 100644
>>> --- a/fs/btrfs/qgroup.c
>>> +++ b/fs/btrfs/qgroup.c
>>> @@ -1069,21 +1069,24 @@ static void report_reserved_underflow(struct
>>> btrfs_fs_info *fs_info,
>>> #endif
>>> qgroup->reserved = 0;
>>> }
>>> +
>>> /*
>>> - * The easy accounting, if we are adding/removing the only ref for an
>>> extent
>>> - * then this qgroup and all of the parent qgroups get their reference and
>>> - * exclusive counts adjusted.
>>> + * The easy accounting, we're updating qgroup relationship whose child
>>> qgroup
>>> + * only have exclusive extents.
>>> + * In this case, we only need to update the rfer/excl, and inherit rsv from
>>> + * child qgroup (@src)
>>> *
>>> * Caller should hold fs_info->qgroup_lock.
>>> */
>>> static int __qgroup_excl_accounting(struct btrfs_fs_info *fs_info,
>>> struct ulist *tmp, u64 ref_root,
>>> - u64 num_bytes, int sign)
>>> + struct btrfs_qgroup *src, int sign)
>>> {
>>> struct btrfs_qgroup *qgroup;
>>> struct btrfs_qgroup_list *glist;
>>> struct ulist_node *unode;
>>> struct ulist_iterator uiter;
>>> + u64 num_bytes = src->excl;
>>> int ret = 0;
>>>
>>> qgroup = find_qgroup_rb(fs_info, ref_root);
>>> @@ -1096,13 +1099,12 @@ static int __qgroup_excl_accounting(struct
>>> btrfs_fs_info *fs_info,
>>> WARN_ON(sign < 0 && qgroup->excl < num_bytes);
>>> qgroup->excl += sign * num_bytes;
>>> qgroup->excl_cmpr += sign * num_bytes;
>>> - if (sign > 0) {
>>> - trace_qgroup_update_reserve(fs_info, qgroup, -(s64)num_bytes);
>>> - if (qgroup->reserved < num_bytes)
>>> - report_reserved_underflow(fs_info, qgroup, num_bytes);
>>> - else
>>> - qgroup->reserved -= num_bytes;
>>> - }
>>> +
>>> + /* *Inherit* qgroup rsv info from @src */
>>> + if (sign > 0)
>>> + qgroup_rsv_increase_by_qgroup(qgroup, src);
>>> + else
>>> + qgroup_rsv_decrease_by_qgroup(qgroup, src);
>>
>>
>> I'm a bit confused by the semantics of the 'sign' variable. So what you
>> are doing is that if sign is > 0 then you are "adding a relationship"
>> i.e. adding 'src reservation to 'qgroup', presumably because the src is
>> a child of qgroup? So you are handling both adding and deletion in the
>> if statement?
>
> Yes, the original design of @sign is to allow single function to handle
> both relationship adding and deleting.
> just like the rest code, which uses @sign to handle both adding and
> deleting without using if.
>
>>
>> However, before that apparently only deleting a relation ship was
>> handled by that same if (And I believe that was wrong since if sign > 0
>> then we should be adding bytes but here we are subtracting). SO the bug
>> being fixed by this commit are actually 2 bugs:
>>
>> 1. Completely missing the "adding a relation ship case"
>> 2. Incorrect hanlding of sign < 0, since this was handled by the sign >
>> 0 case?
>
> Yes, in fact 2 bugs.
>
> Although the original code is acting like it's allocating space inside
> the new parent, so it reduces parent's reserved, and adding new excl/refer.
>
> However it's not the case, it should do inheriting, not allocating from
> parent.
>
> For sign > 0, (adding relationship) parent should inherit all excl/rfer
> and reserved space.
> For sign < 0, (deleting relationshio) parent should have all its
> excl/rfer along with reserved space removed.
>
> ^^^ This should be the correct behavior.
In that case I think this explanation needs to go into the commit
message itself.
>
> The original code is just a copy of older code, as you can see in commit
> 9c8b35b1ba21 ("btrfs: quota: Automatically update related qgroups or
> mark INCONSISTENT flags when assigning/deleting a qgroup relations.").
You can also add this about how the bug got introduced in the first place.
>
> So it's a bug dating back to ancient days and it's my fault I didn't
> expose it in the very beginning.
>
> Thanks,
> Qu
>>
>>
>>
>>>
>>> qgroup_dirty(fs_info, qgroup);
>>>
>>> @@ -1122,15 +1124,10 @@ static int __qgroup_excl_accounting(struct
>>> btrfs_fs_info *fs_info,
>>> qgroup->rfer_cmpr += sign * num_bytes;
>>> WARN_ON(sign < 0 && qgroup->excl < num_bytes);
>>> qgroup->excl += sign * num_bytes;
>>> - if (sign > 0) {
>>> - trace_qgroup_update_reserve(fs_info, qgroup,
>>> - -(s64)num_bytes);
>>> - if (qgroup->reserved < num_bytes)
>>> - report_reserved_underflow(fs_info, qgroup,
>>> - num_bytes);
>>> - else
>>> - qgroup->reserved -= num_bytes;
>>> - }
>>> + if (sign > 0)
>>> + qgroup_rsv_increase_by_qgroup(qgroup, src);
>>> + else
>>> + qgroup_rsv_decrease_by_qgroup(qgroup, src);
>>> qgroup->excl_cmpr += sign * num_bytes;
>>> qgroup_dirty(fs_info, qgroup);
>>>
>>> @@ -1173,7 +1170,7 @@ static int quick_update_accounting(struct
>>> btrfs_fs_info *fs_info,
>>> if (qgroup->excl == qgroup->rfer) {
>>> ret = 0;
>>> err = __qgroup_excl_accounting(fs_info, tmp, dst,
>>> - qgroup->excl, sign);
>>> + qgroup, sign);
>>> if (err < 0) {
>>> ret = err;
>>> goto out;
>>>
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