Message-ID: <52EA16CD.7070807@linux.vnet.ibm.com>
Date: Thu, 30 Jan 2014 10:09:33 +0100
From: Heinz Graalfs <graalfs@linux.vnet.ibm.com>
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To: Rusty Russell <rusty@rustcorp.com.au>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/6] virtio_blk: don't crash, report error if virtqueue
 is broken.
References: <1389753371-26469-1-git-send-email-rusty@rustcorp.com.au> <1389753371-26469-2-git-send-email-rusty@rustcorp.com.au>
In-Reply-To: <1389753371-26469-2-git-send-email-rusty@rustcorp.com.au>
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Sender: linux-kernel-owner@vger.kernel.org

On 15/01/14 03:36, Rusty Russell wrote:
> A bad implementation of virtio might cause us to mark the virtqueue
> broken: we'll dev_err() in that case, and the device is useless, but
> let's not BUG_ON().
>
> ENOMEM or ENOSPC implies the ring is full, and we should try again
> later (-ENOMEM is documented to happen, but doesn't, as we fall
> through to ENOSPC).
>
> EIO means it's broken.
>
> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
> ---
>   drivers/block/virtio_blk.c | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 6a680d4de7f1..704d6c814c17 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -158,6 +158,7 @@ static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req)
>   	unsigned long flags;
>   	unsigned int num;
>   	const bool last = (req->cmd_flags & REQ_END) != 0;
> +	int err;
>
>   	BUG_ON(req->nr_phys_segments + 2 > vblk->sg_elems);
>
> @@ -198,11 +199,16 @@ static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req)
>   	}
>
>   	spin_lock_irqsave(&vblk->vq_lock, flags);
> -	if (__virtblk_add_req(vblk->vq, vbr, vbr->sg, num) < 0) {
> +	err = __virtblk_add_req(vblk->vq, vbr, vbr->sg, num);
> +	if (err) {
>   		virtqueue_kick(vblk->vq);

the kick might fail here after a request was successfully added.

>   		spin_unlock_irqrestore(&vblk->vq_lock, flags);
>   		blk_mq_stop_hw_queue(hctx);
> -		return BLK_MQ_RQ_QUEUE_BUSY;
> +		/* Out of mem doesn't actually happen, since we fall back
> +		 * to direct descriptors */
> +		if (err == -ENOMEM || err == -ENOSPC)
> +			return BLK_MQ_RQ_QUEUE_BUSY;
> +		return BLK_MQ_RQ_QUEUE_ERROR;
>   	}
>
>   	if (last)
>

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