linux-kernel - Re: [PATCH 3/3] fs: fix corner case race on freeze

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Date:   Thu, 3 May 2018 17:02:17 +0200
From:   Jan Kara <jack@...e.cz>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     viro@...iv.linux.org.uk, linux-fsdevel@...r.kernel.org,
        jack@...e.cz, bart.vanassche@....com, ming.lei@...hat.com,
        rjw@...ysocki.net, mguzik@...hat.com, linux-pm@...r.kernel.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] fs: fix corner case race on freeze_bdev() when sb
 disappears

On Fri 20-04-18 16:59:04, Luis R. Rodriguez wrote:
> freeze_bdev() will bail but leave the bd_fsfreeze_count incremented
> if the get_active_super() does not find the superblock on our
> super_blocks list to match.
> 
> This issue has been present since v2.6.29 during the introduction of the
> ioctl_fsfreeze() and ioctl_fsthaw() via commit fcccf502540e3 ("filesystem
> freeze: implement generic freeze feature").
> 
> I am not aware of any existing races which have triggered this
> situation, however, if it does trigger it could mean leaving a
> superblock with bd_fsfreeze_count always positive.
> 
> Fixes: fcccf502540e3 ("filesystem freeze: implement generic freeze feature")
> Signed-off-by: Luis R. Rodriguez <mcgrof@...nel.org>

Looks good to me. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/block_dev.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index b54966679833..7a532aa58c07 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -507,8 +507,10 @@ struct super_block *freeze_bdev(struct block_device *bdev)
>  	}
>  
>  	sb = get_active_super(bdev);
> -	if (!sb)
> +	if (!sb) {
> +		bdev->bd_fsfreeze_count--;
>  		goto out;
> +	}
>  	if (sb->s_op->freeze_super)
>  		error = sb->s_op->freeze_super(sb);
>  	else
> -- 
> 2.16.3
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR