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

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Date:   Mon, 8 Jun 2020 05:02:19 +0000
From:   "Kohada.Tetsuhiro@...MitsubishiElectric.co.jp" 
        <Kohada.Tetsuhiro@...MitsubishiElectric.co.jp>
To:     'Namjae Jeon' <linkinjeon@...nel.org>
CC:     Namjae Jeon <namjae.jeon@...sung.com>,
        "Mori.Takahiro@...MitsubishiElectric.co.jp" 
        <Mori.Takahiro@...MitsubishiElectric.co.jp>,
        "Motai.Hirotaka@...MitsubishiElectric.co.jp" 
        <Motai.Hirotaka@...MitsubishiElectric.co.jp>,
        Sungjong Seo <sj1557.seo@...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 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.
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)

> > 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>