linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: don't clear CP_QUOTA_NEED_FSCK

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Message-ID: <0e00fefb-d0af-6143-afcd-6d8c8fa34743@huawei.com>
Date:   Fri, 22 Feb 2019 11:27:08 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
CC:     <linux-kernel@...r.kernel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>
Subject: Re: [f2fs-dev] [PATCH] f2fs: don't clear CP_QUOTA_NEED_FSCK_FLAG

On 2019/2/22 10:40, Jaegeuk Kim wrote:
> On 02/20, Chao Yu wrote:
>> On 2019/2/20 15:25, Chao Yu wrote:
>>> On 2019/2/20 15:08, Jaegeuk Kim wrote:
>>>> On 02/18, Chao Yu wrote:
>>>>> On 2019/2/16 12:55, Jaegeuk Kim wrote:
>>>>>> On 02/13, Chao Yu wrote:
>>>>>>> On 2019/2/12 10:33, Jaegeuk Kim wrote:
>>>>>>>> If we met this once, let fsck.f2fs clear this only.
>>>>>>>> Note that, this addresses all the subtle fault injection test.
>>>>>>>>
>>>>>>>> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
>>>>>>>> ---
>>>>>>>>  fs/f2fs/checkpoint.c | 2 --
>>>>>>>>  1 file changed, 2 deletions(-)
>>>>>>>>
>>>>>>>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
>>>>>>>> index 03fea4efd64b..10a3ada28715 100644
>>>>>>>> --- a/fs/f2fs/checkpoint.c
>>>>>>>> +++ b/fs/f2fs/checkpoint.c
>>>>>>>> @@ -1267,8 +1267,6 @@ static void update_ckpt_flags(struct f2fs_sb_info *sbi, struct cp_control *cpc)
>>>>>>>>  
>>>>>>>>  	if (is_sbi_flag_set(sbi, SBI_QUOTA_SKIP_FLUSH))
>>>>>>>>  		__set_ckpt_flags(ckpt, CP_QUOTA_NEED_FSCK_FLAG);
>>>>>>>> -	else
>>>>>>>> -		__clear_ckpt_flags(ckpt, CP_QUOTA_NEED_FSCK_FLAG);
>>>>>>>
>>>>>>> I didn't get it, previously, if we didn't persist all quota file's data in
>>>>>>> checkpoint, then we will tag CP_QUOTA_NEED_FSCK_FLAG in CP area, but in current
>>>>>>> checkpoint, we have persisted all quota file's data, quota files are consistent
>>>>>>> with all other files in filesystem, why we can't remove this NEED_FSCK flag..?
>>>>>>
>>>>>> I said it's subtle. So, I guessed 1) set CP_QUOTA_NEED_FSCK_FLAG, 2) clear
>>>>>
>>>>> I know it's subtle... and I agreed we can fix it like this in upstream
>>>>> first, but in our product, it's not rare that we hit the
>>>>> QUOTA_SKIP_FLUSH(its value is 4) case, later we may encounter long latency
>>>>> caused by quota repairing of fsck.
>>>>>
>>>>>> SBI_QUOTA_SKIP_FLUSH by checkpoint, 3) clear CP_QUOTA_NEED_FSCK_FLAG by another
>>>>>> checkpoint?
>>>>>
>>>>> But later if QUOTA_NEED_REPAIR is set, we will set QUOTA_NEED_FSCK_FLAG
>>>>> again, right?
>>>>>
>>>>> if (is_sbi_flag_set(sbi, SBI_QUOTA_NEED_REPAIR))
>>>>> 	__set_ckpt_flags(ckpt, CP_QUOTA_NEED_FSCK_FLAG);
>>>>>
>>>>>
>>>>> So in order to figure out whether this is caused by out-of-order execution
>>>>> of below assignments:
>>>>>
>>>>> 	if (is_sbi_flag_set(sbi, SBI_QUOTA_SKIP_FLUSH))
>>>>> 		__set_ckpt_flags(ckpt, CP_QUOTA_NEED_FSCK_FLAG);
>>>>> 	else
>>>>> 		__clear_ckpt_flags(ckpt, CP_QUOTA_NEED_FSCK_FLAG); --- clear flag later
>>>>>
>>>>> 	if (is_sbi_flag_set(sbi, SBI_QUOTA_NEED_REPAIR))
>>>>> 		__set_ckpt_flags(ckpt, CP_QUOTA_NEED_FSCK_FLAG); --- set flag first
>>>>>
>>>>>
>>>>> Could you have a try:
>>>>>
>>>>> 	if (is_sbi_flag_set(sbi, SBI_QUOTA_NEED_REPAIR) ||
>>>>> 			is_sbi_flag_set(sbi, SBI_QUOTA_SKIP_FLUSH))
>>>>> 		__set_ckpt_flags(ckpt, CP_QUOTA_NEED_FSCK_FLAG);
>>>>> 	else
>>>>> 		__clear_ckpt_flags(ckpt, CP_QUOTA_NEED_FSCK_FLAG);
>>>>
>>>> What does this mean? I'm in doubt we have a missing case where we clear this
>>>
>>> Cpu pipeline / compiler can make code out-of-order execution, which means:
>>>
>>> a = 1;
>>> b = 2;
>>>
>>> may actually be executed as the order of:
>>>
>>> b = 2;
>>> a = 1;
>>>
>>> So I doubt that below two line codes can be executed out-of-order:
>>>
>>> else
>>> 	__clear_ckpt_flags(ckpt, CP_QUOTA_NEED_FSCK_FLAG); --- clear flag later
>>>
>>> if ()
>>> 	__set_ckpt_flags(ckpt, CP_QUOTA_NEED_FSCK_FLAG); --- set flag first
> 
> In spin_lock_irqsave()?

Not sure in coverage of spin_lock, system can guarantee codes being
executed orderly.

> 
>>>
>>>> flag, CP_QUOTA_NEED_FSCK_FLAG.
>>>
>>> Agreed, I've checked each operation in f2fs_quota_operations yesterday, and
>>> didn't find any missing places yet...
>>
>> Oh, I mean the place where set SBI_QUOTA_NEED_REPAIR, I also doubt we
>> missed to set the flag.
> 
> So, I may need to keep this patch untill we find the missing case. I'll keep an
> eye on this.

Agreed, do you mind adding one line comment there to notice that?

Thanks,

> 
>>
>> Thanks,
>>
>>>
>>> Thanks,
>>>
>>>>
>>>>>
>>>>> Thanks,
>>>>>
>>>>>>
>>>>>>>
>>>>>>> Thanks,
>>>>>>>
>>>>>>>>  
>>>>>>>>  	if (is_sbi_flag_set(sbi, SBI_QUOTA_NEED_REPAIR))
>>>>>>>>  		__set_ckpt_flags(ckpt, CP_QUOTA_NEED_FSCK_FLAG);
>>>>>>>>
>>>>>>
>>>>>> .
>>>>>>
>>>>
>>>> .
>>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> Linux-f2fs-devel mailing list
>>> Linux-f2fs-devel@...ts.sourceforge.net
>>> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
>>>
>>> .
>>>
> 
> .
>