linux-kernel - Re: [RFC PATCH 05/14] nvmet: Send an AEN on CCR completion

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Message-ID: <20251231220020.GK3864520-mkhalfella@purestorage.com>
Date: Wed, 31 Dec 2025 14:00:20 -0800
From: Mohamed Khalfella <mkhalfella@...estorage.com>
To: Sagi Grimberg <sagi@...mberg.me>
Cc: Chaitanya Kulkarni <kch@...dia.com>, Christoph Hellwig <hch@....de>,
	Jens Axboe <axboe@...nel.dk>, Keith Busch <kbusch@...nel.org>,
	Aaron Dailey <adailey@...estorage.com>,
	Randy Jennings <randyj@...estorage.com>,
	John Meneghini <jmeneghi@...hat.com>,
	Hannes Reinecke <hare@...e.de>, linux-nvme@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 05/14] nvmet: Send an AEN on CCR completion

On Sat 2025-12-27 11:48:49 +0200, Sagi Grimberg wrote:
> 
> 
> On 25/12/2025 20:13, Mohamed Khalfella wrote:
> > On Thu 2025-12-25 15:23:51 +0200, Sagi Grimberg wrote:
> >>
> >> On 26/11/2025 4:11, Mohamed Khalfella wrote:
> >>> Send an AEN to initiator when impacted controller exists. The
> >>> notification points to CCR log page that initiator can read to check
> >>> which CCR operation completed.
> >>>
> >>> Signed-off-by: Mohamed Khalfella <mkhalfella@...estorage.com>
> >>> ---
> >>>    drivers/nvme/target/core.c  | 27 +++++++++++++++++++++++----
> >>>    drivers/nvme/target/nvmet.h |  3 ++-
> >>>    include/linux/nvme.h        |  3 +++
> >>>    3 files changed, 28 insertions(+), 5 deletions(-)
> >>>
> >>> diff --git a/drivers/nvme/target/core.c b/drivers/nvme/target/core.c
> >>> index 7dbe9255ff42..60173833c3eb 100644
> >>> --- a/drivers/nvme/target/core.c
> >>> +++ b/drivers/nvme/target/core.c
> >>> @@ -202,7 +202,7 @@ static void nvmet_async_event_work(struct work_struct *work)
> >>>    	nvmet_async_events_process(ctrl);
> >>>    }
> >>>    
> >>> -void nvmet_add_async_event(struct nvmet_ctrl *ctrl, u8 event_type,
> >>> +static void nvmet_add_async_event_locked(struct nvmet_ctrl *ctrl, u8 event_type,
> >>>    		u8 event_info, u8 log_page)
> >>>    {
> >>>    	struct nvmet_async_event *aen;
> >>> @@ -215,12 +215,17 @@ void nvmet_add_async_event(struct nvmet_ctrl *ctrl, u8 event_type,
> >>>    	aen->event_info = event_info;
> >>>    	aen->log_page = log_page;
> >>>    
> >>> -	mutex_lock(&ctrl->lock);
> >>>    	list_add_tail(&aen->entry, &ctrl->async_events);
> >>> -	mutex_unlock(&ctrl->lock);
> >>>    
> >>>    	queue_work(nvmet_wq, &ctrl->async_event_work);
> >>>    }
> >>> +void nvmet_add_async_event(struct nvmet_ctrl *ctrl, u8 event_type,
> >>> +		u8 event_info, u8 log_page)
> >>> +{
> >>> +	mutex_lock(&ctrl->lock);
> >>> +	nvmet_add_async_event_locked(ctrl, event_type, event_info, log_page);
> >>> +	mutex_unlock(&ctrl->lock);
> >>> +}
> >>>    
> >>>    static void nvmet_add_to_changed_ns_log(struct nvmet_ctrl *ctrl, __le32 nsid)
> >>>    {
> >>> @@ -1788,6 +1793,18 @@ struct nvmet_ctrl *nvmet_alloc_ctrl(struct nvmet_alloc_ctrl_args *args)
> >>>    }
> >>>    EXPORT_SYMBOL_GPL(nvmet_alloc_ctrl);
> >>>    
> >>> +static void nvmet_ctrl_notify_ccr(struct nvmet_ctrl *ctrl)
> >>> +{
> >>> +	lockdep_assert_held(&ctrl->lock);
> >>> +
> >>> +	if (nvmet_aen_bit_disabled(ctrl, NVME_AEN_BIT_CCR_COMPLETE))
> >>> +		return;
> >>> +
> >>> +	nvmet_add_async_event_locked(ctrl, NVME_AER_NOTICE,
> >>> +				     NVME_AER_NOTICE_CCR_COMPLETED,
> >>> +				     NVME_LOG_CCR);
> >>> +}
> >>> +
> >>>    static void nvmet_ctrl_complete_pending_ccr(struct nvmet_ctrl *ctrl)
> >>>    {
> >>>    	struct nvmet_subsys *subsys = ctrl->subsys;
> >>> @@ -1801,8 +1818,10 @@ static void nvmet_ctrl_complete_pending_ccr(struct nvmet_ctrl *ctrl)
> >>>    	list_for_each_entry(sctrl, &subsys->ctrls, subsys_entry) {
> >>>    		mutex_lock(&sctrl->lock);
> >>>    		list_for_each_entry(ccr, &sctrl->ccrs, entry) {
> >>> -			if (ccr->ctrl == ctrl)
> >>> +			if (ccr->ctrl == ctrl) {
> >>> +				nvmet_ctrl_notify_ccr(sctrl);
> >>>    				ccr->ctrl = NULL;
> >>> +			}
> >> Is this double loop necessary? Would you have more than one controller
> >> cross resetting the same
> > As it is implemented now CCRs are linked to sctrl. This decision can be
> > revisited if found suboptimal. At some point I had CCRs linked to
> > ctrl->subsys but that led to lock ordering issues. Double loop is
> > necessary to find all CCRs in all controllers and mark them done.
> > Yes, it is possible to have more than one sctrl resetting the same
> > ictrl.
> 
> I'm more interested in simplifying.
> 
> >
> >> controller? Won't it be better to install a callback+opaque that the
> >> controller removal will call?
> > Can you elaborate more on that? Better in what terms?
> >
> > nvmet_ctrl_complete_pending_ccr() is called from nvmet_ctrl_free() when
> > we know that ctrl->ref is zero and no new CCRs will be added to this
> > controller because nvmet_ctrl_find_get_ccr() will not be able to get it.
> 
> In nvmet, the controller is serving a single host. Hence I am not sure I
> understand how multiple source controllers will try to reset the impacted
> controller. So, if there is a 1-1 relationship between source and impacted
> controller, I'd perhaps suggest to simplify and install on the impacted 
> controller
> callback+opaque (e.g. void *data) instead of having it iterate and then 
> actually send
> the AEN from the impacted controller.

A controller is serving a single path for a given host. A host that is
connected to nvme subsystem via multiple paths will have more than one
controller. I can think of two reasons why we need to support resetting
an impacted controller from multiple source controllers.

- It is possible for multiple paths to go down at the same time. The
  first source controller we use for CCR, even though we check to see if
  LIVE, might have lost connection to subsystem. It is a matter of time
  for it to see keepalive timeout and fail too. If CCR fails using this
  controller we should not give up. We need to try other paths.

- Some nvme subsystems might support resetting impacted controller from
  a subset of controllers connected to the host. An array that has
  multiple frontend engines might not support resetting controllers
  across engines. In fact, TP8028 allows for subsystem to suggest to
  host to use another source controller in Alternate Controller ID
  (ACID) fied on CCR logpage (not implemente in this patchset).