Re: multipath-tools: add ANA support for NVMe device

[Hannes Reinecke]

On 11/14/18 6:47 PM, Mike Snitzer wrote:
> On Wed, Nov 14 2018 at  2:49am -0500,
> Hannes Reinecke <hare@xxxxxxx> wrote:
> 
>> On 11/14/18 6:38 AM, Mike Snitzer wrote:
>>> On Tue, Nov 13 2018 at  1:00pm -0500,
>>> Mike Snitzer <snitzer@xxxxxxxxxx> wrote:
>>>
>>>> [1]: http://lists.infradead.org/pipermail/linux-nvme/2018-November/020765.html
>>>> [2]: https://www.redhat.com/archives/dm-devel/2018-November/msg00072.html
>>> ...
>>>
>>> I knew there had to be a pretty tight coupling between the NVMe driver's
>>> native multipathing and ANA support... and that the simplicity of
>>> Hannes' patch [1] was too good to be true.
>>>
>>> The real justification for not making Hannes' change is it'd effectively
>>> be useless without first splitting out the ANA handling done during NVMe
>>> request completion (NVME_SC_ANA_* cases in nvme_failover_req) that
>>> triggers re-reading the ANA log page accordingly.
>>>
>>> So without the ability to drive the ANA workqueue to trigger
>>> nvme_read_ana_log() from the nvme driver's completion path -- even if
>>> nvme_core.multipath=N -- it really doesn't buy multipath-tools anything
>>> to have the NVMe driver export the ana state via sysfs, because that ANA
>>> state will never get updated.
>>>
>> Hmm. Indeed, I was more focussed on having the sysfs attributes
>> displayed, so yes, indeed it needs some more work.
> ...
>>> Not holding my breath BUT:
>>> if decoupling the reading of ANA state from native NVMe multipathing
>>> specific work during nvme request completion were an acceptable
>>> advancement I'd gladly do the work.
>>>
>> I'd be happy to work on that, given that we'll have to have 'real'
>> ANA support for device-mapper anyway for SLE12 SP4 etc.
> 
> I had a close enough look yesterday that I figured I'd just implement
> what I reasoned through as one way forward, compile tested only (patch
> relative to Jens' for-4.21/block):
> 
>  drivers/nvme/host/core.c      | 14 +++++++---
>  drivers/nvme/host/multipath.c | 65 ++++++++++++++++++++++++++-----------------
>  drivers/nvme/host/nvme.h      |  4 +++
>  3 files changed, 54 insertions(+), 29 deletions(-)
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index f172d63db2b5..05313ab5d91e 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -252,10 +252,16 @@ void nvme_complete_rq(struct request *req)
>  	trace_nvme_complete_rq(req);
>  
>  	if (unlikely(status != BLK_STS_OK && nvme_req_needs_retry(req))) {
> -		if ((req->cmd_flags & REQ_NVME_MPATH) &&
> -		    blk_path_error(status)) {
> -			nvme_failover_req(req);
> -			return;
> +		if (blk_path_error(status)) {
> +			struct nvme_ns *ns = req->q->queuedata;
> +			u16 nvme_status = nvme_req(req)->status;
> +
> +			if (req->cmd_flags & REQ_NVME_MPATH) {
> +				nvme_failover_req(req);
> +				nvme_update_ana(ns, nvme_status);
> +				return;
> +			}
> +			nvme_update_ana(ns, nvme_status);
>  		}
>  
>  		if (!blk_queue_dying(req->q)) {
> diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
> index 5e3cc8c59a39..f7fbc161dc8c 100644
> --- a/drivers/nvme/host/multipath.c
> +++ b/drivers/nvme/host/multipath.c
> @@ -22,7 +22,7 @@ MODULE_PARM_DESC(multipath,
>  
>  inline bool nvme_ctrl_use_ana(struct nvme_ctrl *ctrl)
>  {
> -	return multipath && ctrl->subsys && (ctrl->subsys->cmic & (1 << 3));
> +	return ctrl->subsys && (ctrl->subsys->cmic & (1 << 3));
>  }
>  
>  /*
> @@ -47,6 +47,17 @@ void nvme_set_disk_name(char *disk_name, struct nvme_ns *ns,
>  	}
>  }
>  
> +static bool nvme_ana_error(u16 status)
> +{
> +	switch (status & 0x7ff) {
> +	case NVME_SC_ANA_TRANSITION:
> +	case NVME_SC_ANA_INACCESSIBLE:
> +	case NVME_SC_ANA_PERSISTENT_LOSS:
> +		return true;
> +	}
> +	return false;
> +}
> +
>  void nvme_failover_req(struct request *req)
>  {
>  	struct nvme_ns *ns = req->q->queuedata;
> @@ -58,10 +69,7 @@ void nvme_failover_req(struct request *req)
>  	spin_unlock_irqrestore(&ns->head->requeue_lock, flags);
>  	blk_mq_end_request(req, 0);
>  
> -	switch (status & 0x7ff) {
> -	case NVME_SC_ANA_TRANSITION:
> -	case NVME_SC_ANA_INACCESSIBLE:
> -	case NVME_SC_ANA_PERSISTENT_LOSS:
> +	if (nvme_ana_error(status)) {
>  		/*
>  		 * If we got back an ANA error we know the controller is alive,
>  		 * but not ready to serve this namespaces.  The spec suggests
> @@ -69,31 +77,38 @@ void nvme_failover_req(struct request *req)
>  		 * that the admin and I/O queues are not serialized that is
>  		 * fundamentally racy.  So instead just clear the current path,
>  		 * mark the the path as pending and kick of a re-read of the ANA
> -		 * log page ASAP.
> +		 * log page ASAP (see nvme_update_ana() below).
>  		 */
>  		nvme_mpath_clear_current_path(ns);
> -		if (ns->ctrl->ana_log_buf) {
> -			set_bit(NVME_NS_ANA_PENDING, &ns->flags);
> -			queue_work(nvme_wq, &ns->ctrl->ana_work);
> +	} else {
> +		switch (status & 0x7ff) {
> +		case NVME_SC_HOST_PATH_ERROR:
> +			/*
> +			 * Temporary transport disruption in talking to the
> +			 * controller.  Try to send on a new path.
> +			 */
> +			nvme_mpath_clear_current_path(ns);
> +			break;
> +		default:
> +			/*
> +			 * Reset the controller for any non-ANA error as we
> +			 * don't know what caused the error.
> +			 */
> +			nvme_reset_ctrl(ns->ctrl);
> +			break;
>  		}
> -		break;
> -	case NVME_SC_HOST_PATH_ERROR:
> -		/*
> -		 * Temporary transport disruption in talking to the controller.
> -		 * Try to send on a new path.
> -		 */
> -		nvme_mpath_clear_current_path(ns);
> -		break;
> -	default:
> -		/*
> -		 * Reset the controller for any non-ANA error as we don't know
> -		 * what caused the error.
> -		 */
> -		nvme_reset_ctrl(ns->ctrl);
> -		break;
>  	}
Maybe move nvme_mpath_clear_current_path() out of the loop (it wouldn't
matter if we clear the path if we reset the controller afterwards); that
might even clean up the code even more.

> +}
>  
> -	kblockd_schedule_work(&ns->head->requeue_work);
> +void nvme_update_ana(struct nvme_ns *ns, u16 status)
> +{
> +	if (nvme_ana_error(status) && ns->ctrl->ana_log_buf) {
> +		set_bit(NVME_NS_ANA_PENDING, &ns->flags);
> +		queue_work(nvme_wq, &ns->ctrl->ana_work);
> +	}
> +
> +	if (multipath)
> +		kblockd_schedule_work(&ns->head->requeue_work);
>  }

maybe use 'ns->head->disk' here; we only need to call this if we have a
multipath disk.

Remaining bits are okay.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
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