linux-kernel - Re: [PATCH] update sb->s_frozen when freezing read-only mounted device, too

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Message-ID: <961aa3350710050620q42eb6192wdacce1510cc76a4b@mail.gmail.com>
Date:	Fri, 5 Oct 2007 22:20:55 +0900
From:	"Akinobu Mita" <akinobu.mita@...il.com>
To:	"Christoph Hellwig" <hch@....de>
Cc:	linux-kernel@...r.kernel.org, xfs@....sgi.com,
	"Tim Shimmin" <xfs-masters@....sgi.com>,
	"David Chinner" <dgc@....com>
Subject: Re: [PATCH] update sb->s_frozen when freezing read-only mounted device, too

2007/10/5, Christoph Hellwig <hch@....de>:
> On Sat, Sep 29, 2007 at 07:09:12PM +0900, Akinobu Mita wrote:
> > freeze_bdev() with the device which is mounted as read only
> > does not change sb->s_frozen from SB_UNFROZEN to SB_FREEZE_TRANS.
> >
> > Because of this behavior, xfs_freeze can break read-only XFS filesystem.
> >
> > Because xfs_thaw does nothing for the filesystem whose sb->s_frozen is
> > SB_UNFROZEN. So freezed readonly XFS filesystem will never be unfreezed.
> > Then we cannot do any unmount/remount operations for that filesystem.
> >
> > This patch updates sb->s_frozen when freeze_bdev() is called for read-only
> > mounted device, too.
>
> I think this fix is valid, but it might be a tad cleaner to just
> set s_frozen to SB_FREEZE_TRANS directly in a separate branch, ala:

It looks cleaner than mine. I'll resubmit it.

> struct super_block *freeze_bdev(struct block_device *bdev)
> {
>         struct super_block *sb;
>
>         down(&bdev->bd_mount_sem);
>         sb = get_super(bdev);
>         if (!sb)
>                 goto out;
>
>         if (sb->s_flags & MS_RDONLY) {
>                 sb->s_frozen = SB_FREEZE_TRANS;
>                 smp_wmb();
>                 goto out;
>         }
>
>         sb->s_frozen = SB_FREEZE_WRITE;
>         smp_wmb();
>
>         __fsync_super(sb);
>
>         sb->s_frozen = SB_FREEZE_TRANS
>         smp_wmb();
>
>         sync_blockdev(sb->s_bdev);
>
>         if (sb->s_op->write_super_lockfs)
>                 sb->s_op->write_super_lockfs(sb);
>
>  out:
>         sync_blockdev(bdev);
>         return sb;      /* thaw_bdev releases s->s_umount and bd_mount_sem */
> }
>
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