linux-kernel - Re: [PATCH] block: make sure FSEQ_DATA request has the same rq

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Date:	Fri, 03 Sep 2010 14:47:36 +0900
From:	Kiyoshi Ueda <k-ueda@...jp.nec.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Mike Snitzer <snitzer@...hat.com>, jaxboe@...ionio.com,
	j-nomura@...jp.nec.com, jamie@...reable.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-raid@...r.kernel.org, hch@....de
Subject: Re: [PATCH] block: make sure FSEQ_DATA request has the same rq_disk
 as the original

Hi Tejun,

On 09/03/2010 02:43 AM +0900, Tejun Heo wrote:
> rq->rq_disk and bio->bi_bdev->bd_disk may differ if a request has
> passed through remapping drivers.  FSEQ_DATA request incorrectly
> followed bio->bi_bdev->bd_disk ending up being issued w/ mismatching
> rq_disk.  Make it follow orig_rq->rq_disk.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Reported-by: Kiyoshi Ueda <k-ueda@...jp.nec.com>
> ---
> Kiyoshi, can you please apply this patch on top and verify that the
> problem goes away?  The reason I and Mike didn't see the problem was
> because we were using REQ_FUA capable underlying device, which makes
> block layer bypass sequencing for FSEQ_DATA request.
> 
> Thanks.
> 
>  block/blk-flush.c |    7 +++++++
>  1 file changed, 7 insertions(+)
> 
> Index: block/block/blk-flush.c
> ===================================================================
> --- block.orig/block/blk-flush.c
> +++ block/block/blk-flush.c
> @@ -111,6 +111,13 @@ static struct request *queue_next_fseq(s
>  		break;
>  	case QUEUE_FSEQ_DATA:
>  		init_request_from_bio(rq, orig_rq->bio);
> +		/*
> +		 * orig_rq->rq_disk may be different from
> +		 * bio->bi_bdev->bd_disk if orig_rq got here through
> +		 * remapping drivers.  Make sure rq->rq_disk points
> +		 * to the same one as orig_rq.
> +		 */
> +		rq->rq_disk = orig_rq->rq_disk;
>  		rq->cmd_flags &= ~(REQ_FLUSH | REQ_FUA);
>  		rq->cmd_flags |= orig_rq->cmd_flags & (REQ_FLUSH | REQ_FUA);
>  		rq->end_io = flush_data_end_io;

Ah, I see, thank you for the quick fix!
I confirmed no panic occurs with this patch.

Tested-by: Kiyoshi Ueda <k-ueda@...jp.nec.com>


By the way, I had been considering a block-layer interface which remaps
struct request and its bios to a block device such as:
void blk_remap_request(struct request *rq, struct block_device *bdev)
{
	rq->rq_disk = bdev->bd_disk;

	__rq_for_each_bio(bio, rq) {
		bio->bi_bdev = bdev->bd_disk;
	}
}

If there is such an interface and remapping drivers use it, then these
kind of issues may be avoided in the future.

Thanks,
Kiyoshi Ueda
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