linux-kernel - RE: [PATCH] exfat: remove EXFAT_SB

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Date:   Fri, 12 Jun 2020 17:34:46 +0900
From:   "Sungjong Seo" <sj1557.seo@...sung.com>
To:     "'Tetsuhiro Kohada'" <kohada.t2@...il.com>
Cc:     <kohada.tetsuhiro@...mitsubishielectric.co.jp>,
        <mori.takahiro@...mitsubishielectric.co.jp>,
        <motai.hirotaka@...mitsubishielectric.co.jp>,
        "'Namjae Jeon'" <namjae.jeon@...sung.com>,
        <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] exfat: remove EXFAT_SB_DIRTY flag

> remove EXFAT_SB_DIRTY flag and related codes.
> 
> This flag is set/reset in exfat_put_super()/exfat_sync_fs() to avoid
> sync_blockdev().
> However ...
> - exfat_put_super():
> Before calling this, the VFS has already called sync_filesystem(), so sync
> is never performed here.
> - exfat_sync_fs():
> After calling this, the VFS calls sync_blockdev(), so, it is meaningless
> to check EXFAT_SB_DIRTY or to bypass sync_blockdev() here.
> Not only that, but in some cases can't clear VOL_DIRTY.
> ex:
> VOL_DIRTY is set when rmdir starts, but when non-empty-dir is detected,
> return error without setting EXFAT_SB_DIRTY.
> If performe 'sync' in this state, VOL_DIRTY will not be cleared.
> 
> Remove the EXFAT_SB_DIRTY check to ensure synchronization.
> And, remove the code related to the flag.
> 
> Signed-off-by: Tetsuhiro Kohada <kohada.t2@...il.com>
> ---
>  fs/exfat/balloc.c   |  4 ++--
>  fs/exfat/dir.c      | 16 ++++++++--------
>  fs/exfat/exfat_fs.h |  5 +----
>  fs/exfat/fatent.c   |  7 ++-----
>  fs/exfat/misc.c     |  3 +--
>  fs/exfat/namei.c    | 12 ++++++------
>  fs/exfat/super.c    | 11 +++--------
>  7 files changed, 23 insertions(+), 35 deletions(-)
> 
[snip]
> 
> @@ -62,11 +59,9 @@ static int exfat_sync_fs(struct super_block *sb, int
> wait)
> 
>  	/* If there are some dirty buffers in the bdev inode */
>  	mutex_lock(&sbi->s_lock);
> -	if (test_and_clear_bit(EXFAT_SB_DIRTY, &sbi->s_state)) {
> -		sync_blockdev(sb->s_bdev);
> -		if (exfat_set_vol_flags(sb, VOL_CLEAN))
> -			err = -EIO;
> -	}

I looked through most codes related to EXFAT_SB_DIRTY and VOL_DIRTY.
And your approach looks good because all of them seem to be protected by
s_lock.

BTW, as you know, sync_filesystem() calls sync_fs() with 'nowait' first,
and then calls it again with 'wait' twice. No need to sync with lock twice.
If so, isn't it okay to do nothing when wait is 0?

> +	sync_blockdev(sb->s_bdev);
> +	if (exfat_set_vol_flags(sb, VOL_CLEAN))
> +		err = -EIO;
>  	mutex_unlock(&sbi->s_lock);
>  	return err;
>  }
> --
> 2.25.1