linux-kernel - Re: [f2fs-dev] [PATCH v3] f2fs: avoid race condition for shinker count

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Message-ID: <20201117164021.GA1636127@google.com>
Date:   Tue, 17 Nov 2020 08:40:21 -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, kernel-team@...roid.com,
        Light Hsieh <Light.Hsieh@...iatek.com>
Subject: Re: [f2fs-dev] [PATCH v3] f2fs: avoid race condition for shinker
 count

On 11/12, Chao Yu wrote:
> On 2020/11/12 13:40, Jaegeuk Kim wrote:
> > Light reported sometimes shinker gets nat_cnt < dirty_nat_cnt resulting in
> > wrong do_shinker work. Let's avoid to get stale data by using nat_tree_lock.
> > 
> > Reported-by: Light Hsieh <Light.Hsieh@...iatek.com>
> > Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> > ---
> > v3:
> >   - fix to use NM_I(sbi)
> > 
> >   fs/f2fs/shrinker.c | 6 +++++-
> >   1 file changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/f2fs/shrinker.c b/fs/f2fs/shrinker.c
> > index d66de5999a26..555712ba06d8 100644
> > --- a/fs/f2fs/shrinker.c
> > +++ b/fs/f2fs/shrinker.c
> > @@ -18,7 +18,11 @@ static unsigned int shrinker_run_no;
> >   static unsigned long __count_nat_entries(struct f2fs_sb_info *sbi)
> >   {
> > -	long count = NM_I(sbi)->nat_cnt - NM_I(sbi)->dirty_nat_cnt;
> > +	long count;
> > +
> > +	down_read(&NM_I(sbi)->nat_tree_lock);
> > +	count = NM_I(sbi)->nat_cnt - NM_I(sbi)->dirty_nat_cnt;
> > +	up_read(&NM_I(sbi)->nat_tree_lock);
> >   	return count > 0 ? count : 0;
> 
> Minor thing,
> 
> Just return count is enough? since count should never be smaller than 0.

Yeah, but let me keep this just in case.

> 
> Anyway,
> 
> Reviewed-by: Chao Yu <yuchao0@...wei.com>
> 
> Thanks,
> 
> Thanks,
> 
> >   }
> >