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

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Message-ID: <4aae85c2-1829-06c0-8fd1-4148100dc0b9@huawei.com>
Date:   Thu, 12 Nov 2020 14:57:22 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>, <linux-kernel@...r.kernel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>, <kernel-team@...roid.com>
CC:     Light Hsieh <Light.Hsieh@...iatek.com>
Subject: Re: [f2fs-dev] [PATCH v3] f2fs: avoid race condition for shinker
 count

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.

Anyway,

Reviewed-by: Chao Yu <yuchao0@...wei.com>

Thanks,

Thanks,

>   }
>