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

[Christoph Hellwig <hch@xxxxxx>]

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:

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 */
}