Re: [PATCH v3 08/21] nvme: Implement cross-controller reset recovery

[Mohamed Khalfella]

On Mon 2026-02-16 13:41:39 +0100, Hannes Reinecke wrote:
> On 2/14/26 05:25, 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@xxxxxxxxxxxxxxx>
> > ---
> >   drivers/nvme/host/constants.c |   1 +
> >   drivers/nvme/host/core.c      | 141 ++++++++++++++++++++++++++++++++++
> >   drivers/nvme/host/nvme.h      |   9 +++
> >   3 files changed, 151 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 231d402e9bfb..765b1524b3ed 100644
> > --- a/drivers/nvme/host/core.c
> > +++ b/drivers/nvme/host/core.c
> > @@ -554,6 +554,146 @@ 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)
> > +{
> > +	struct nvme_ccr_entry ccr = { };
> > +	union nvme_result res = { 0 };
> > +	struct nvme_command c = { };
> > +	unsigned long flags, tmo;
> > +	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;
> > +
> > +	tmo = secs_to_jiffies(ictrl->kato);
> > +	if (!wait_for_completion_timeout(&ccr.complete, tmo)) {
> > +		ret = -ETIMEDOUT;
> > +		goto out;
> > +	}
> > +
> That will be tricky. The 'ccr' comand will be sent with the default
> command queue timeout which is decoupled from KATO.
> So you really should set the command timeout for the 'ccr' command
> to ctrl->kato to ensure it'll be terminated correctly.
> 

Agreed. The timeout for CCR request should be ctr->kato just like what
we do for keep alive request. The easiest way IMO to do is is to extend
__nvme_submit_sync_cmd() to take request timeout. I do not want to make
this change in this patchset.

Is it okay I make this change after this patchset gets merged?