linux-kernel - RE: [PATCH 3/3] exfat: set EXFAT_SB_DIRTY and VOL

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Date:   Tue, 9 Jun 2020 11:02:57 +0900
From:   "Namjae Jeon" <namjae.jeon@...sung.com>
To:     <Kohada.Tetsuhiro@...MitsubishiElectric.co.jp>
Cc:     <Mori.Takahiro@...MitsubishiElectric.co.jp>,
        <Motai.Hirotaka@...MitsubishiElectric.co.jp>,
        "'Sungjong Seo'" <sj1557.seo@...sung.com>,
        <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        "'Namjae Jeon'" <linkinjeon@...nel.org>
Subject: RE: [PATCH 3/3] exfat: set EXFAT_SB_DIRTY and VOL_DIRTY at the same
 timing

> Thank you for your comment.
> 
> > >> Can you split this patch into two? (Don't set VOL_DIRTY on
> > >> -ENOTEMPTY and Setting EXFAT_SB_DIRTY is merged into
> > >> exfat_set_vol_flag). I need to check the second one more.
> > >
> > > Can't do that.
> > >
> > > exfat_set_vol_flag() is called when rmdir processing begins. When
> > > Not-empty is detected, VOL_DIRTY has already been written and synced
> > > to the media.
> > You can move it before calling exfat_remove_entries().
> 
> Can be moved, but that doesn't solve the problem.
> It causes the similar problem as before.
> 
> exfat_remove_entries() calls exfat_get_dentry().
> If exfat_get_dentry() fails, update bh and set SB_DIRTY will not be executed.
> As a result, SB_DIRTY is not set and sync does not work.
> Similar problems occur with other writing functions.
> Similar problems occur when pre-write checks are added in the future.
> 
> If you don't set VOL_DIRTY at the beginning, you should delay to set VOL_DIRTY until update-bh & set
> SB_DIRTY.
> This avoids unnecessary changes to VOL_DIRTY/VOL_CLEAN.
Right, That's what I am going to point out.
> I think this method is smart, but it is difficult to decide when to set VOL_CLEAN.
> (I tried to implement it, but gave up)
Okay, I'm a little busy now, but I'll give you feedback soon.
Thanks for your work!
> 
> > > By doing this, sync is guaranteed if VOL_DIRTY is set by calling
> > > exfat_set_vol_flag.
> > >
> > > This change may still have problems, but it's little better than
> > > before, I think.
> > I need to check more if it is the best or there is more better way.
> 
> I think the sync-problems still exist.
> Let's improve little by little. :-)
> 
> BR
> ---
> Kohada Tetsuhiro <Kohada.Tetsuhiro@...MitsubishiElectric.co.jp>