Re: [RFC 3/9] fsfreeze: Prevent emergency thaw from looping infinitely

[Eric Sandeen <sandeen@redhat.com>]

On 9/13/12 6:03 AM, Fernando Luis Vázquez Cao wrote:
> The thawing of a filesystem through sysrq-j loops infinitely as it
> incorrectly detects a thawed filesytsem as frozen and tries to
> unfreeze repeatedly. This is a regression caused by
> 4504230a71566785a05d3e6b53fa1ee071b864eb ("freeze_bdev: grab active
> reference to frozen superblocks") in that it no longer returned
> -EINVAL for superblocks that were not frozen.
> 
> Return -EINVAL when the filesystem is already unfrozen to avoid this
> problem.
> 
> Cc: Josef Bacik <jbacik@fusionio.com>
> Cc: Eric Sandeen <sandeen@redhat.com>
> Cc: Christoph Hellwig <hch@infradead.org>
> Reviewed-by: Jan Kara <jack@suse.cz>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>

Reviewed-by: Eric Sandeen <sandeen@redhat.com>

I actually sent a simpler (but less cleaned up) version of this 2 years ago,
I guess it got missed and I didn't notice.  So thanks!

-Eric

> ---
> 
> diff -urNp vfs-orig/fs/block_dev.c vfs/fs/block_dev.c
> --- vfs-orig/fs/block_dev.c	2012-07-04 18:57:54.000000000 +0900
> +++ vfs/fs/block_dev.c	2012-07-12 13:22:38.124815295 +0900
> @@ -319,22 +319,17 @@ int thaw_bdev(struct block_device *bdev,
>  	if (!bdev->bd_fsfreeze_count)
>  		goto out;
>  
> -	error = 0;
> -	if (--bdev->bd_fsfreeze_count > 0)
> -		goto out;
> -
> -	if (!sb)
> +	if (--bdev->bd_fsfreeze_count > 0 || !sb) {
> +		error = 0;
>  		goto out;
> +	}
>  
>  	error = thaw_super(sb);
> -	if (error) {
> +	if (error)
>  		bdev->bd_fsfreeze_count++;
> -		mutex_unlock(&bdev->bd_fsfreeze_mutex);
> -		return error;
> -	}
>  out:
>  	mutex_unlock(&bdev->bd_fsfreeze_mutex);
> -	return 0;
> +	return error;
>  }
>  EXPORT_SYMBOL(thaw_bdev);
>  
> 
> 

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