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

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Date:   Mon, 15 Jun 2020 11:59:51 +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

> On 2020/06/12 17:34, Sungjong Seo wrote:
> >> 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?
> 
> I also think  ‘do nothing when wait is 0’ as you say, but I'm still not
> sure.
> 
> Some other Filesystems do nothing with nowait and just return.
> However, a few Filesystems always perform sync.
> 
> sync_blockdev() waits for completion, so it may be inappropriate to call
> with  nowait. (But it was called in the original code)
> 
> I'm still not sure, so I excluded it in this patch.
> Is it okay to include it?
> 

Yes, I think so. sync_filesystem() will call __sync_blockdev() without 'wait' first.
So, it's enough to call sync_blockdev() with s_lock just one time.

> 
> >> +	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
> >
> >
> 
> BR
> ---
> Tetsuhiro Kohada <kohada.t2@...il.com>