[PATCH] nvme-rdma: fix timeout handler

[hch@lst.de (Christoph Hellwig)]

On Thu, Dec 13, 2018@01:29:17PM -0800, Sagi Grimberg wrote:
> Currently, we have several problems with the timeout
> handler:
> 1. If we timeout on the controller establishment flow, we will
> hang because we don't execute the error recovery (and we shouldn't
> because the create_ctrl flow needs to fail and cleanup on its own)
> 2. We might also hang if we get a disconnet on a queue while the
> controller is already deleting. This racy flow can cause the
> controller disable/shutdown admin command to hang.
> 
> We cannot complete a timed out request from the timeout handler
> without mutual exclusion from the teardown flow (e.g.
> nvme_rdma_error_recovery_work). So we serialize it in the
> timeout handler and stop the queue to guarantee that no
> one races with us from completing the request.
> 
> Reported-by: Jaesoo Lee <jalee at purestorage.com>
> Signed-off-by: Sagi Grimberg <sagi at grimberg.me>
> ---
>  drivers/nvme/host/rdma.c | 33 +++++++++++++++++++++++----------
>  1 file changed, 23 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/nvme/host/rdma.c b/drivers/nvme/host/rdma.c
> index 80b3113b45fb..af8f4cedabc1 100644
> --- a/drivers/nvme/host/rdma.c
> +++ b/drivers/nvme/host/rdma.c
> @@ -1080,12 +1080,13 @@ static void nvme_rdma_error_recovery_work(struct work_struct *work)
>  	nvme_rdma_reconnect_or_remove(ctrl);
>  }
>  
> -static void nvme_rdma_error_recovery(struct nvme_rdma_ctrl *ctrl)
> +static int nvme_rdma_error_recovery(struct nvme_rdma_ctrl *ctrl)
>  {
>  	if (!nvme_change_ctrl_state(&ctrl->ctrl, NVME_CTRL_RESETTING))
> -		return;
> +		return -EBUSY;
>  
>  	queue_work(nvme_wq, &ctrl->err_work);
> +	return 0;
>  }
>  
>  static void nvme_rdma_wr_error(struct ib_cq *cq, struct ib_wc *wc,
> @@ -1693,18 +1694,30 @@ static enum blk_eh_timer_return
>  nvme_rdma_timeout(struct request *rq, bool reserved)
>  {
>  	struct nvme_rdma_request *req = blk_mq_rq_to_pdu(rq);
> +	struct nvme_rdma_queue *queue = req->queue;
> +	struct nvme_rdma_ctrl *ctrl = queue->ctrl;
> +
> +	dev_warn(ctrl->ctrl.device, "I/O %d QID %d timeout\n",
> +		 rq->tag, nvme_rdma_queue_idx(queue));
>  
> +	if (nvme_rdma_error_recovery(req->queue->ctrl)) {
> +		union nvme_result res = {};
>  
> +		nvme_rdma_stop_queue(queue);
> +		flush_work(&ctrl->err_work);
>  
> +		/*
> +		 * now no-one is competing with us, safely check if the
> +		 * was completed and fail it if not.
> +		 */
> +		if (READ_ONCE(rq->state) != MQ_RQ_COMPLETE) {
> +			nvme_req(rq)->flags |= NVME_REQ_CANCELLED;
> +			nvme_end_request(rq, NVME_SC_ABORT_REQ, res);
> +			return BLK_EH_DONE;
> +		}

So why did nvme_rdma_error_recovery not complete this request?
I think that is where our problem is, and we are just papering over it.