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

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Message-ID: <TY2PR01MB28755044132E6FCF00F68FFF909C0@TY2PR01MB2875.jpnprd01.prod.outlook.com>
Date:   Mon, 15 Jun 2020 08:31:22 +0000
From:   "Kohada.Tetsuhiro@...MitsubishiElectric.co.jp" 
        <Kohada.Tetsuhiro@...MitsubishiElectric.co.jp>
To:     "'sj1557.seo@...sung.com'" <sj1557.seo@...sung.com>
CC:     "Mori.Takahiro@...MitsubishiElectric.co.jp" 
        <Mori.Takahiro@...MitsubishiElectric.co.jp>,
        "Motai.Hirotaka@...MitsubishiElectric.co.jp" 
        <Motai.Hirotaka@...MitsubishiElectric.co.jp>,
        'Namjae Jeon' <namjae.jeon@...sung.com>,
        "'linux-fsdevel@...r.kernel.org'" <linux-fsdevel@...r.kernel.org>,
        "'linux-kernel@...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.

OK.
I will repost v2-patch with the 'wait' check added.
Thanks for your comment.


> > >> +	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
---
Kohada Tetsuhiro <Kohada.Tetsuhiro@...MitsubishiElectric.co.jp>