Message-ID: <528a39a9-f087-461f-9f5b-c4b5821396b6@suse.de>
Date: Tue, 3 Feb 2026 06:19:51 +0100
From: Hannes Reinecke <hare@...e.de>
To: Mohamed Khalfella <mkhalfella@...estorage.com>,
 Justin Tee <justin.tee@...adcom.com>,
 Naresh Gottumukkala <nareshgottumukkala83@...il.com>,
 Paul Ely <paul.ely@...adcom.com>, Chaitanya Kulkarni <kch@...dia.com>,
 Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>,
 Keith Busch <kbusch@...nel.org>, Sagi Grimberg <sagi@...mberg.me>
Cc: Aaron Dailey <adailey@...estorage.com>,
 Randy Jennings <randyj@...estorage.com>,
 Dhaval Giani <dgiani@...estorage.com>, linux-nvme@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 08/14] nvme: Implement cross-controller reset recovery

On 1/30/26 23:34, 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@...estorage.com>
> ---
>   drivers/nvme/host/constants.c |   1 +
>   drivers/nvme/host/core.c      | 129 ++++++++++++++++++++++++++++++++++
>   drivers/nvme/host/nvme.h      |   9 +++
>   3 files changed, 139 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 3e1e02822dd4..13e0775d56b4 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -554,6 +554,134 @@ 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 *sctrl;
> +	unsigned long flags;
> +
> +	mutex_lock(&nvme_subsystems_lock);
> +	list_for_each_entry(sctrl, &subsys->ctrls, subsys_entry) {
> +		if (sctrl->cntlid < min_cntlid)
> +			continue;
> +
> +		if (atomic_dec_if_positive(&sctrl->ccr_limit) < 0)
> +			continue;
> +
> +		spin_lock_irqsave(&sctrl->lock, flags);
> +		if (sctrl->state != NVME_CTRL_LIVE) {
> +			spin_unlock_irqrestore(&sctrl->lock, flags);
> +			atomic_inc(&sctrl->ccr_limit);
> +			continue;
> +		}
> +
> +		/*
> +		 * We got a good candidate source controller that is locked and
> +		 * LIVE. However, no guarantee sctrl will not be deleted after
> +		 * sctrl->lock is released. Get a ref of both sctrl and admin_q
> +		 * so they do not disappear until we are done with them.
> +		 */
> +		WARN_ON_ONCE(!blk_get_queue(sctrl->admin_q));
> +		nvme_get_ctrl(sctrl);
> +		spin_unlock_irqrestore(&sctrl->lock, flags);
> +		goto found;
> +	}
> +	sctrl = NULL;
> +found:

Normally one would be using a temporary loop variable and assign 'sctrl' 
to that one if found. Then you can just call 'break' and drop the 'goto'.

> +	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)
> +{
> +	struct nvme_ccr_entry ccr = { };
> +	union nvme_result res = { 0 };
> +	struct nvme_command c = { };
> +	unsigned long flags, tmo;
> +	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)
> +		goto out;
> +
> +	result = le32_to_cpu(res.u32);
> +	if (result & 0x01) /* Immediate Reset Successful */
> +		goto out;
> +
> +	tmo = msecs_to_jiffies(max(ictrl->cqt, ictrl->kato * 1000));
> +	if (!wait_for_completion_timeout(&ccr.complete, tmo)) {
> +		ret = -ETIMEDOUT;
> +		goto out;
> +	}
> +
> +	if (ccr.ccrs != NVME_CCR_STATUS_SUCCESS)
> +		ret = -EREMOTEIO;
> +out:
> +	spin_lock_irqsave(&sctrl->lock, flags);
> +	list_del(&ccr.list);
> +	spin_unlock_irqrestore(&sctrl->lock, flags);
> +	return ret;
> +}
> +
> +unsigned long nvme_fence_ctrl(struct nvme_ctrl *ictrl)
> +{
> +	unsigned long deadline, now, 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);
> +
> +	now = jiffies;
> +	deadline = now + msecs_to_jiffies(timeout);
> +	while (time_before(now, deadline)) {
> +		sctrl = nvme_find_ctrl_ccr(ictrl, min_cntlid);
> +		if (!sctrl) {
> +			/* CCR failed, switch to time-based recovery */
> +			return deadline - now;
> +		}
> +
> +		ret = nvme_issue_wait_ccr(sctrl, ictrl);
> +		if (!ret) {
> +			dev_info(ictrl->device, "CCR succeeded using %s\n",
> +				 dev_name(sctrl->device));
> +			nvme_put_ctrl_ccr(sctrl);
> +			return 0;
> +		}
> +
> +		/* CCR failed, try another path */
> +		min_cntlid = sctrl->cntlid + 1;
> +		nvme_put_ctrl_ccr(sctrl);
> +		now = jiffies;
> +	}

That will spin until 'deadline' is reached if 'nvme_issue_wait_ccr()' 
returns an error. _And_ if the CCR itself runs into a timeout we would
never have tried another path (which could have succeeded).

I'd rather rework this loop to open-code 'issue_and_wait()' in the loop,
and only switch to the next controller if the submission of CCR failed.
Once that is done we can 'just' wait for completion, as a failure there
will be after KATO timeout anyway and any subsequent CCR would be pointless.

> +
> +	dev_info(ictrl->device, "CCR reached timeout, call it done\n");
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(nvme_fence_ctrl);
> +
>   bool nvme_change_ctrl_state(struct nvme_ctrl *ctrl,
>   		enum nvme_ctrl_state new_state)
>   {
> @@ -5119,6 +5247,7 @@ int nvme_init_ctrl(struct nvme_ctrl *ctrl, struct device *dev,
>   
>   	mutex_init(&ctrl->scan_lock);
>   	INIT_LIST_HEAD(&ctrl->namespaces);
> +	INIT_LIST_HEAD(&ctrl->ccr_list);
>   	xa_init(&ctrl->cels);
>   	ctrl->dev = dev;
>   	ctrl->ops = ops;
> diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
> index 00866bbc66f3..fa18f580d76a 100644
> --- a/drivers/nvme/host/nvme.h
> +++ b/drivers/nvme/host/nvme.h
> @@ -279,6 +279,13 @@ enum nvme_ctrl_flags {
>   	NVME_CTRL_FROZEN		= 6,
>   };
>   
> +struct nvme_ccr_entry {
> +	struct list_head list;
> +	struct completion complete;
> +	struct nvme_ctrl *ictrl;
> +	u8 ccrs;
> +};
> +
 >   struct nvme_ctrl {>   	bool comp_seen;
>   	bool identified;
> @@ -296,6 +303,7 @@ struct nvme_ctrl {
>   	struct blk_mq_tag_set *tagset;
>   	struct blk_mq_tag_set *admin_tagset;
>   	struct list_head namespaces;
> +	struct list_head ccr_list;
>   	struct mutex namespaces_lock;
>   	struct srcu_struct srcu;
>   	struct device ctrl_device;
> @@ -814,6 +822,7 @@ blk_status_t nvme_host_path_error(struct request *req);
>   bool nvme_cancel_request(struct request *req, void *data);
>   void nvme_cancel_tagset(struct nvme_ctrl *ctrl);
>   void nvme_cancel_admin_tagset(struct nvme_ctrl *ctrl);
> +unsigned long nvme_fence_ctrl(struct nvme_ctrl *ctrl);
>   bool nvme_change_ctrl_state(struct nvme_ctrl *ctrl,
>   		enum nvme_ctrl_state new_state);
>   int nvme_disable_ctrl(struct nvme_ctrl *ctrl, bool shutdown);

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@...e.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich

Powered by blists - more mailing lists