linux-kernel - Re: [PATCH 2/2] blkdev: check for valid request queue before issuing flush

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Date:	Tue, 13 Jul 2010 14:55:14 +0200
From:	Jens Axboe <axboe@...nel.dk>
To:	Dave Chinner <david@...morbit.com>
CC:	xfs@....sgi.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] blkdev: check for valid request queue before issuing
 flush

On 2010-07-13 09:50, Dave Chinner wrote:
> From: Dave Chinner <dchinner@...hat.com>
> 
> Issuing a blkdev_issue_flush() on an unconfigured loop device causes a panic as
> q->make_request_fn is not configured. This can occur when trying to mount the
> unconfigured loop device as an XFS filesystem. There are no guards that catch
> the bio before the request function is called because we don't add a payload to
> the bio. Instead, manually check this case as soon as we have a pointer to the
> queue to flush.
> 
> Signed-off-by: Dave Chinner <dchinner@...hat.com>
> ---
>  block/blk-barrier.c |    9 +++++++++
>  1 files changed, 9 insertions(+), 0 deletions(-)
> 
> diff --git a/block/blk-barrier.c b/block/blk-barrier.c
> index 0d710c9..0fd766e 100644
> --- a/block/blk-barrier.c
> +++ b/block/blk-barrier.c
> @@ -319,6 +319,15 @@ int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
>  	if (!q)
>  		return -ENXIO;
>  
> +	/*
> +	 * some block devices may not have their queue correctly set up here
> +	 * (e.g. loop device without a backing file) and so issuing a flush
> +	 * here will panic. Ensure there is a request function before issuing
> +	 * the barrier.
> +	 */
> +	if (!q->make_request_fn)
> +		return -ENXIO;
> +
>  	bio = bio_alloc(gfp_mask, 0);
>  	bio->bi_end_io = bio_end_empty_barrier;
>  	bio->bi_bdev = bdev;

This may appear ugly, but I think the patch is fine since there's not
much we can do about the loop crap (outside of changing how you do
setup/configure of it).

I'll apply this, thanks.

-- 
Jens Axboe

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