Re: [PATCH] btrfs: qgroup: Auto kick in rescan if qgroup tree is initialized without rescan initialized

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On 2018年07月26日 15:21, Misono Tomohiro wrote:
> On 2018/07/26 15:59, Qu Wenruo wrote:
>> Under certain case, btrfs/166 could cause power loss just after quota
>> tree initialized but rescan not kicked in.
>>
>> In this case, since flags of qgroup status item is just ON |
>> INCONSISTENT, without RESCAN flag, rescan won't be kicked in in next
>> mount.
>>
>> Now kick in rescan automatically for such situation, so user won't need
>> to do rescan manually.
> 
> How about setting all of BTRFS_QGROUP_STATUS_FLAG_ON/INCONSISTENT/RESCAN
> at first place and calling qgroup_rescan_init(fs_info, 0, 0) 
> (currently it is (fs_info, 0, 1)) in btrfs_quota_enable()?

I'm wondering if there will any race window between we set RESCAN flag
and we really kick in rescan.

But the idea looks doable and I'll look into it.

> 
> I think with this approach, current btrfs-progs can work as expected too.

In theory, we still need to fix btrfs check/kernel since we may need to
handle old fs.
But since it's pretty rare, I think if we could fix kernel using the
idea you purposed, it would be enough for this case.

Thanks,
Qu

> 
>>
>> Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
>> ---
>>  fs/btrfs/qgroup.c | 11 +++++++++++
>>  1 file changed, 11 insertions(+)
>>
>> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
>> index c25dc47210a3..e62598fc354f 100644
>> --- a/fs/btrfs/qgroup.c
>> +++ b/fs/btrfs/qgroup.c
>> @@ -392,6 +392,17 @@ int btrfs_read_qgroup_config(struct btrfs_fs_info *fs_info)
>>  			fs_info->qgroup_flags = btrfs_qgroup_status_flags(l,
>>  									  ptr);
>>  			rescan_progress = btrfs_qgroup_status_rescan(l, ptr);
>> +
>> +			/*
>> +			 * Qgroup is enabled but rescan hans't kicked in and
>> +			 * power loss happened, kick rescan in
>> +			 */
>> +			if (rescan_progress == 0 &&
>> +			    (BTRFS_QGROUP_STATUS_FLAG_INCONSISTENT |
>> +			     BTRFS_QGROUP_STATUS_FLAG_ON) ==
>> +			    fs_info->qgroup_flags)
>> +				fs_info->qgroup_flags |=
>> +					BTRFS_QGROUP_STATUS_FLAG_RESCAN;
>>  			goto next1;
>>  		}
>>  
>>
> 
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