Re: Exclusive quota of snapshot exceeded despite no space used

[Qu Wenruo <quwenruo@cn.fujitsu.com>]

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