linux-kernel - Re: [PATCH 3/6] f2fs: fix to avoid race condition when updating sbi flag

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Date:   Mon, 19 Sep 2016 14:40:58 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <chao@...nel.org>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Chao Yu <yuchao0@...wei.com>
Subject: Re: [PATCH 3/6] f2fs: fix to avoid race condition when updating sbi
 flag

Hi Chao,

On Sun, Sep 18, 2016 at 11:30:05PM +0800, Chao Yu wrote:
> From: Chao Yu <yuchao0@...wei.com>
> 
> Making updating of sbi flag atomic by using {test,set,clear}_bit,
> otherwise in concurrency scenario, the flag could be updated incorrectly.
> 
> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> ---
>  fs/f2fs/f2fs.h | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index 9b4bbf2..c30f744b 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -794,7 +794,7 @@ struct f2fs_sb_info {
>  	struct proc_dir_entry *s_proc;		/* proc entry */
>  	struct f2fs_super_block *raw_super;	/* raw super block pointer */
>  	int valid_super_block;			/* valid super block no */
> -	int s_flag;				/* flags for sbi */
> +	unsigned long s_flag;				/* flags for sbi */
>  
>  #ifdef CONFIG_F2FS_FS_ENCRYPTION
>  	u8 key_prefix[F2FS_KEY_DESC_PREFIX_SIZE];
> @@ -1063,17 +1063,19 @@ static inline struct address_space *NODE_MAPPING(struct f2fs_sb_info *sbi)
>  
>  static inline bool is_sbi_flag_set(struct f2fs_sb_info *sbi, unsigned int type)
>  {
> -	return sbi->s_flag & (0x01 << type);
> +	return test_bit(type, &sbi->s_flag);
>  }
>  
>  static inline void set_sbi_flag(struct f2fs_sb_info *sbi, unsigned int type)
>  {
> -	sbi->s_flag |= (0x01 << type);
> +	if (!test_bit(type, &sbi->s_flag))
> +		set_bit(type, &sbi->s_flag);

The set_bit() is enough, no?

>  }
>  
>  static inline void clear_sbi_flag(struct f2fs_sb_info *sbi, unsigned int type)
>  {
> -	sbi->s_flag &= ~(0x01 << type);
> +	if (test_bit(type, &sbi->s_flag))
> +		clear_bit(type, &sbi->s_flag);

ditto.

Thanks,

>  }
>  
>  static inline unsigned long long cur_cp_version(struct f2fs_checkpoint *cp)
> -- 
> 2.7.2