Re: Exclusive quota of snapshot exceeded despite no space used

[Johannes Henninger <johannes+btrfs@henninger.io>]

On 27.10.2015 02:06, Qu Wenruo wrote:
>
>
> Johannes Henninger wrote on 2015/10/27 01:15 +0100:
>> On 26.10.2015 08:12, Qu Wenruo wrote:
>>>
>>>>>> Thanks a lot for your reply!
>>>>>>
>>>>>> While remounting the filesystem fixes the issue temporary, it
>>>>>> doesn't
>>>>>> take very long for the bug to happen again so it's not really a
>>>>>> workaround I can work with.
>>>>>>
>>>>>> I did recompile the kernel using your patches, but unfortunately the
>>>>>> problem still appears.
>>>>>>
>>>>>> Thanks,
>>>>>> Johannes
>>>>>>
>>>>> Interesting, just touching file will cause EQUOTA is quite a big
>>>>> problem.
>>>>>
>>>>> I'll try to reproduce it with my patchset and see what really caused
>>>>> the problem.
>>>>> The problem seems to do with snapshot qgroup hacking.
>>>>> But I'm not completely sure yet.
>>>>>
>>>>> BTW, does "sync; btrfs qgroup show -prce" still show excl as 16K?
>>>>> 16K is the correct number with only 6 empty files, just in case.
>>>>>
>>>>> Thanks,
>>>>> Qu
>>>>
>>>> I ran my example from the first mail again and managed to write 7
>>>> files
>>>> this time, "qgroup show" still shows 16kB after sync:
>>>>
>>>> root@t420:/media/extern/snap# btrfs qg limit -e 50M .
>>>> root@t420:/media/extern/snap# for file in {1..100}; do touch $file;
>>>> sleep 5m; done
>>>> touch: cannot touch ‘8’: Disk quota exceeded
>>>> ^C
>>>> root@t420:/media/extern/snap# sync
>>>> root@t420:/media/extern/snap# btrfs qgroup show -pcre .
>>>> qgroupid         rfer         excl     max_rfer     max_excl parent
>>>> child
>>>> --------         ----         ----     --------     -------- ------
>>>> -----
>>>> 0/5          16.00KiB     16.00KiB         none         none
>>>> ---     ---
>>>> 0/257        16.00KiB     16.00KiB         none         none
>>>> ---     ---
>>>> 0/258        16.00KiB     16.00KiB         none     50.00MiB
>>>> ---     ---
>>>> root@t420:/media/extern/snap# btrfs fi sync .
>>>> FSSync '.'
>>>> root@t420:/media/extern/snap# btrfs qgroup show -pcre .
>>>> qgroupid         rfer         excl     max_rfer     max_excl parent
>>>> child
>>>> --------         ----         ----     --------     -------- ------
>>>> -----
>>>> 0/5          16.00KiB     16.00KiB         none         none
>>>> ---     ---
>>>> 0/257        16.00KiB     16.00KiB         none         none
>>>> ---     ---
>>>> 0/258        16.00KiB     16.00KiB         none     50.00MiB
>>>> ---     ---
>>>>
>>>> By the way, I don't if its relevant but the problem is not limited to
>>>> exclusive quotas, but also happens when setting a "referenced" limit
>>>> (qgroup limit without "-e").
>>>>
>>>> Thanks,
>>>> Johannes
>>>>
>>>
>>> The bug is located, and turns out to be quite a stupid problem caused
>>> by myself.
>>>
>>> I just forgot to include a cleanup patch during rebase!!!! AGAIN!!!
>>>
>>> You can apply the following patch to resolve it:
>>> [PATCH 3/3] btrfs: qgroup: Fix a rebase bug which will cause qgroup
>>> double free
>>>
>>> Or just apply the whole patchset:
>>> [4.4][PATCH 0/3] btrfs: Qgroup hotfix
>>>
>>> At least, with the patchset based on Chris' integration-4.4 branch, it
>>> succeeded in touching all the 100 files in my test box.
>>>
>>> Thanks,
>>> Qu
>>>
>>
>> It's working! Thank you so much for fixing this bug, you don't even know
>> how much this has helped me!
>>
>> Thanks!
>> Johannes
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> Glad to hear that.
>
> If it's working for you, it would be better to add a 'Tested-by' tag
> for the 3rd patch.
>
> Thanks,
> Qu

Sure! Is there anything I have to do? I'm a kernel and mailing list noob :)

Thanks,
Johannes