Re: [PATCH v4 08/15] nvme: Implement cross-controller reset recovery

[Hannes Reinecke <hare@suse.de>]

On 3/28/26 01:43, Mohamed Khalfella wrote:
> A host that has more than one path connecting to an nvme subsystem
> typically has an nvme controller associated with every path. This is
> mostly applicable to nvmeof. If one path goes down, inflight IOs on that
> path should not be retried immediately on another path because this
> could lead to data corruption as described in TP4129. TP8028 defines
> cross-controller reset mechanism that can be used by host to terminate
> IOs on the failed path using one of the remaining healthy paths. Only
> after IOs are terminated, or long enough time passes as defined by
> TP4129, inflight IOs should be retried on another path. Implement core
> cross-controller reset shared logic to be used by the transports.
> 
> Signed-off-by: Mohamed Khalfella <mkhalfella@purestorage.com>
> ---
>   drivers/nvme/host/constants.c |   1 +
>   drivers/nvme/host/core.c      | 145 ++++++++++++++++++++++++++++++++++
>   drivers/nvme/host/nvme.h      |   9 +++
>   3 files changed, 155 insertions(+)
> 
> diff --git a/drivers/nvme/host/constants.c b/drivers/nvme/host/constants.c
> index dc90df9e13a2..f679efd5110e 100644
> --- a/drivers/nvme/host/constants.c
> +++ b/drivers/nvme/host/constants.c
> @@ -46,6 +46,7 @@ static const char * const nvme_admin_ops[] = {
>   	[nvme_admin_virtual_mgmt] = "Virtual Management",
>   	[nvme_admin_nvme_mi_send] = "NVMe Send MI",
>   	[nvme_admin_nvme_mi_recv] = "NVMe Receive MI",
> +	[nvme_admin_cross_ctrl_reset] = "Cross Controller Reset",
>   	[nvme_admin_dbbuf] = "Doorbell Buffer Config",
>   	[nvme_admin_format_nvm] = "Format NVM",
>   	[nvme_admin_security_send] = "Security Send",
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 824a1193bec8..5603ae36444f 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -554,6 +554,150 @@ void nvme_cancel_admin_tagset(struct nvme_ctrl *ctrl)
>   }
>   EXPORT_SYMBOL_GPL(nvme_cancel_admin_tagset);
>   
> +static struct nvme_ctrl *nvme_find_ctrl_ccr(struct nvme_ctrl *ictrl,
> +					    u32 min_cntlid)
> +{
> +	struct nvme_subsystem *subsys = ictrl->subsys;
> +	struct nvme_ctrl *ctrl, *sctrl = NULL;
> +	unsigned long flags;
> +
> +	mutex_lock(&nvme_subsystems_lock);
> +	list_for_each_entry(ctrl, &subsys->ctrls, subsys_entry) {
> +		if (ctrl->cntlid < min_cntlid)
> +			continue;
> +
> +		if (atomic_dec_if_positive(&ctrl->ccr_limit) < 0)
> +			continue;
> +
> +		spin_lock_irqsave(&ctrl->lock, flags);
> +		if (ctrl->state != NVME_CTRL_LIVE) {
> +			spin_unlock_irqrestore(&ctrl->lock, flags);
> +			atomic_inc(&ctrl->ccr_limit);
> +			continue;
> +		}
> +
> +		/*
> +		 * We got a good candidate source controller that is locked and
> +		 * LIVE. However, no guarantee ctrl will not be deleted after
> +		 * ctrl->lock is released. Get a ref of both ctrl and admin_q
> +		 * so they do not disappear until we are done with them.
> +		 */
> +		WARN_ON_ONCE(!blk_get_queue(ctrl->admin_q));
> +		nvme_get_ctrl(ctrl);
> +		spin_unlock_irqrestore(&ctrl->lock, flags);
> +		sctrl = ctrl;
> +		break;
> +	}
> +	mutex_unlock(&nvme_subsystems_lock);
> +	return sctrl;
> +}
> +
> +static void nvme_put_ctrl_ccr(struct nvme_ctrl *sctrl)
> +{
> +	atomic_inc(&sctrl->ccr_limit);
> +	blk_put_queue(sctrl->admin_q);
> +	nvme_put_ctrl(sctrl);
> +}
> +
> +static int nvme_issue_wait_ccr(struct nvme_ctrl *sctrl, struct nvme_ctrl *ictrl,
> +			       unsigned long deadline)
> +{
> +	struct nvme_ccr_entry ccr = { };
> +	union nvme_result res = { 0 };
> +	struct nvme_command c = { };
> +	unsigned long flags, now, tmo = 0;
> +	bool completed = false;
> +	int ret = 0;
> +	u32 result;
> +
> +	init_completion(&ccr.complete);
> +	ccr.ictrl = ictrl;
> +
> +	spin_lock_irqsave(&sctrl->lock, flags);
> +	list_add_tail(&ccr.list, &sctrl->ccr_list);
> +	spin_unlock_irqrestore(&sctrl->lock, flags);
> +
> +	c.ccr.opcode = nvme_admin_cross_ctrl_reset;
> +	c.ccr.ciu = ictrl->ciu;
> +	c.ccr.icid = cpu_to_le16(ictrl->cntlid);
> +	c.ccr.cirn = cpu_to_le64(ictrl->cirn);
> +	ret = __nvme_submit_sync_cmd(sctrl->admin_q, &c, &res,
> +				     NULL, 0, NVME_QID_ANY, 0);
> +	if (ret) {
> +		ret = -EIO;
> +		goto out;
> +	}
> +
> +	result = le32_to_cpu(res.u32);
> +	if (result & 0x01) /* Immediate Reset Successful */
> +		goto out;
> +
> +	now = jiffies;
> +	if (time_before(now, deadline))
> +		tmo = min_t(unsigned long,
> +			    secs_to_jiffies(ictrl->kato), deadline - now);
> +
> +	if (!wait_for_completion_timeout(&ccr.complete, tmo)) {
> +		ret = -ETIMEDOUT;
> +		goto out;
> +	}
> +
> +	completed = true;
> +
> +out:
> +	spin_lock_irqsave(&sctrl->lock, flags);
> +	list_del(&ccr.list);
> +	spin_unlock_irqrestore(&sctrl->lock, flags);
> +	if (completed) {
> +		if (ccr.ccrs == NVME_CCR_STATUS_SUCCESS)
> +			return 0;
> +		return -EREMOTEIO;
> +	}
> +	return ret;
> +}
> +
> +int nvme_fence_ctrl(struct nvme_ctrl *ictrl)
> +{
> +	unsigned long deadline, timeout;
> +	struct nvme_ctrl *sctrl;
> +	u32 min_cntlid = 0;
> +	int ret;
> +
> +	timeout = nvme_fence_timeout_ms(ictrl);
> +	dev_info(ictrl->device, "attempting CCR, timeout %lums\n", timeout);
> +
> +	deadline = jiffies + msecs_to_jiffies(timeout);
> +	while (time_is_after_jiffies(deadline)) {
> +		sctrl = nvme_find_ctrl_ccr(ictrl, min_cntlid);
> +		if (!sctrl) {
> +			dev_dbg(ictrl->device,
> +				"failed to find source controller\n");
> +			return -EIO;
> +		}
> +
> +		ret = nvme_issue_wait_ccr(sctrl, ictrl, deadline);
> +		if (!ret) {
> +			dev_info(ictrl->device, "CCR succeeded using %s\n",
> +				 dev_name(sctrl->device));
> +			nvme_put_ctrl_ccr(sctrl);
> +			return 0;
> +		}
> +
> +		min_cntlid = sctrl->cntlid + 1;
> +		nvme_put_ctrl_ccr(sctrl);
> +
> +		if (ret == -EIO) /* CCR command failed */
> +			continue;
> +
> +		/* CCR operation failed or timed out */
> +		return ret;
> +	}
> +
> +	dev_info(ictrl->device, "CCR operation timeout\n");
> +	return -ETIMEDOUT;
> +}

Please restructure the loop.
Having a comment 'CCR operation failed or timed out',
returning a status, and then have a comment
'CCR operation timeout' _after_ the return is confusing.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@suse.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
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