On 2020/2/7 下午11:59, Anand Jain wrote:
> 
> 
> On 7/2/20 8:15 PM, Qu Wenruo wrote:
>>
>>
>> On 2020/2/7 下午8:01, Anand Jain wrote:
>>> On some systems btrfs/179 fails as the check finds that there is
>>> difference in the qgroup counts.
>>>
>>> By the async nature of qgroup tree scan, the latest qgroup counts at the
>>> time of umount might not be upto date,
>>
>> Yes, so far so good.
>>
>>> if it isn't then the check will
>>> report the difference in count. The difference in qgroup counts are
>>> anyway
>>> updated in the following mount, so it is not a real issue that this test
>>> case is trying to verify.
>>
>> No problem either.
>>
>>> So make sure the qgroup counts are updated
>>> before unmount happens and make the check happy.
>>
>> But the solution doesn't look correct to me.
>>
>> We should either make btrfs-check to handle such half-dropped case
>> better,
> 
>  Check is ok. The count as check counts matches with the count after the
> mount. So what is recorded in the qgroup is not upto date.

Nope. Qgroup records what's in commit tree. For unmounted fs, there is
no difference in commit tree and current tree.

Thus the qgroup scan in btrfs-progs is different from kernel.
Please go check how the btrfs-progs code to see how the difference comes.

> 
>> or find a way to wait for all subvolume drop to be finished in
>> test case.
> 
> Yes this is one way. Just wait for few seconds will do, test passes. Do
> you know any better way?

I didn't remember when, but it looks like `btrfs fi sync` used to wait
for snapshot drop.
But not now. If we have a way to wait for cleaner to finish, we can
solve it pretty easily.

Thanks,
Qu

> 
> Thanks, Anand
> 
>> Papering the test by rescan is not a good idea at all.
>> If one day we really hit some qgroup accounting problem, this papering
>> way could hugely reduce the coverage.
>>
> 
> 
>> Thanks,
>> Qu
>>
>>>
>>> Signed-off-by: Anand Jain <anand.jain@oracle.com>
>>> ---
>>>   tests/btrfs/179 | 8 ++++++++
>>>   1 file changed, 8 insertions(+)
>>>
>>> diff --git a/tests/btrfs/179 b/tests/btrfs/179
>>> index 4a24ea419a7e..74e91841eaa6 100755
>>> --- a/tests/btrfs/179
>>> +++ b/tests/btrfs/179
>>> @@ -109,6 +109,14 @@ wait $snapshot_pid
>>>   kill $delete_pid
>>>   wait $delete_pid
>>>   +# By the async nature of qgroup tree scan, the latest qgroup
>>> counts at the time
>>> +# of umount might not be upto date, if it isn't then the check will
>>> report the
>>> +# difference in count. The difference in qgroup counts are anyway
>>> updated in the
>>> +# following mount, so it is not a real issue that this test case is
>>> trying to
>>> +# verify. So make sure the qgroup counts are updated before unmount
>>> happens.
>>> +
>>> +$BTRFS_UTIL_PROG quota rescan -w $SCRATCH_MNT >> $seqres.full
>>> +
>>>   # success, all done
>>>   echo "Silence is golden"
>>>  
>>