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Date:   Tue, 26 Feb 2019 09:57:26 -0800
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
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 02/22, Chao Yu wrote:
> 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?

       /*
        * TODO: we count on fsck.f2fs to clear this flag until we figure out
        * missing cases which clear it incorrectly.
        */

I added like this.

Thanks,


> 
> 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
> >>>
> >>> .
> >>>
> > 
> > .
> > 

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