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From:   Hyunchul Lee <hyc.lee@gmail.com>
Date:   Mon, 15 Jun 2020 11:10:24 +0900
Message-ID: <CANFS6bYm_yCLG2kKfn8wYBJ4bO+Z+2+R-gHQ6dTwiP9Ut3yy5g@mail.gmail.com>
Subject: Re: [PATCH 1/2] exfat: call sync_filesystem for read-only remount
To:     Namjae Jeon <namjae.jeon@samsung.com>
Cc:     linux-fsdevel@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
        Sungjong Seo <sj1557.seo@samsung.com>
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Hi Namjae,

2020=EB=85=84 6=EC=9B=94 15=EC=9D=BC (=EC=9B=94) =EC=98=A4=EC=A0=84 9:14, N=
amjae Jeon <namjae.jeon@samsung.com>=EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=B1:
>
> Hi Hyunchul,
> > We need to commit dirty metadata and pages to disk before remounting ex=
fat as read-only.
> >
> > This fixes a failure in xfstests generic/452
> Could you please elaborate more the reason why generic/452 in xfstests fa=
iled ?

xfstests generic/452 does the following.
cp /bin/ls <exfat>/
mount -o remount,ro <exfat>

the <exfat>/ls file is corrupted, because while exfat is remounted as read-=
only,
exfat doesn't have a chance to commit metadata and vfs invalidates page
caches in a block device.

I will put this explanation in a commit message.

> >
> > Signed-off-by: Hyunchul Lee <hyc.lee@gmail.com>
> > ---
> >  fs/exfat/super.c | 19 +++++++++++++++++++
> >  1 file changed, 19 insertions(+)
> >
> > diff --git a/fs/exfat/super.c b/fs/exfat/super.c index e650e65536f8..61=
c6cf240c19 100644
> > --- a/fs/exfat/super.c
> > +++ b/fs/exfat/super.c
> > @@ -693,10 +693,29 @@ static void exfat_free(struct fs_context *fc)
> >       }
> >  }
> >
> > +static int exfat_reconfigure(struct fs_context *fc) {
> > +     struct super_block *sb =3D fc->root->d_sb;
> > +     int ret;
> int ret =3D 0;
> > +     bool new_rdonly;
> > +
> > +     new_rdonly =3D fc->sb_flags & SB_RDONLY;
> > +     if (new_rdonly !=3D sb_rdonly(sb)) {
> If you modify it like this, would not we need new_rdonly?
>         if (fc->sb_flags & SB_RDONLY && !sb_rdonly(sb))
>
This condition means that mount options are changed from "rw" to "ro",
or "ro" to "rw".

> > +             if (new_rdonly) {

And this condition means these options are changed from "rw" to "ro".
It seems better to change two conditions to the one you suggested, or
remove those. because sync_filesystem returns 0 when the filesystem is
mounted as read-only.

> > +                     /* volume flag will be updated in exfat_sync_fs *=
/
> > +                     ret =3D sync_filesystem(sb);
> > +                     if (ret < 0)
> > +                             return ret;
> I think that this ret check can be removed by using return ret; below ?

Okay, I will apply this.
Thank you for your comments!


> > +             }
> > +     }
> > +     return 0;
> return ret;
> > +}
> > +
> >  static const struct fs_context_operations exfat_context_ops =3D {
> >       .parse_param    =3D exfat_parse_param,
> >       .get_tree       =3D exfat_get_tree,
> >       .free           =3D exfat_free,
> > +     .reconfigure    =3D exfat_reconfigure,
> >  };
> >
> >  static int exfat_init_fs_context(struct fs_context *fc)
> > --
> > 2.17.1
>
>