linux-kernel - Re: [PATCH 1/5] fsfreeze: Prevent emergency thaw from looping infinitely

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Date:	Mon, 14 Jun 2010 11:18:15 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Dave Chinner <david@...morbit.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	viro@...IV.linux.org.uk, josef@...hat.com, jeffmerkey@...il.com
Subject: Re: [PATCH 1/5] fsfreeze: Prevent emergency thaw from looping
 infinitely

On Thu, Jun 10, 2010 at 05:19:50PM +1000, Dave Chinner wrote:
> Return -EINVAL when the filesystem is already unfrozen to avoid this
> problem.


This includes some additional changes in addition to the description,
and at least one of them seems incorrect.

> -	error = 0;
> -	if (--bdev->bd_fsfreeze_count > 0)
> +	if (!sb)
>  		goto out;
>  
> -	if (!sb)
> +	error = 0;
> +	if (--bdev->bd_fsfreeze_count > 0)
>  		goto out;

Here you reorder the sb check to be before the counter decrement.  But
we do support calling freeze_bdev on a device without a superblock, and
you would leak bd_fsfreeze_count for that case and wrongly return
-EINVAL on unthaw for these now.

>  	error = thaw_super(sb);
> -	if (error) {
> +	if (error)
>  		bdev->bd_fsfreeze_count++;
> -		mutex_unlock(&bdev->bd_fsfreeze_mutex);
> -		return error;
> -	}

Ok, useful cleanup.

>  out:
>  	mutex_unlock(&bdev->bd_fsfreeze_mutex);
> -	return 0;
> +	return error;

And this is the actual fix of course, also looks good.

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