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SubjectRe: multipath-tools: add ANA support for NVMe device
On Wed, Nov 14 2018 at  2:49am -0500,
Hannes Reinecke <hare@suse.de> wrote:

> On 11/14/18 6:38 AM, Mike Snitzer wrote:
> >On Tue, Nov 13 2018 at 1:00pm -0500,
> >Mike Snitzer <snitzer@redhat.com> 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;
}
+}

- 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);
}

void nvme_kick_requeue_lists(struct nvme_ctrl *ctrl)
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 32a1f1cfdfb4..8b4bc2054b7a 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -468,6 +468,7 @@ bool nvme_ctrl_use_ana(struct nvme_ctrl *ctrl);
void nvme_set_disk_name(char *disk_name, struct nvme_ns *ns,
struct nvme_ctrl *ctrl, int *flags);
void nvme_failover_req(struct request *req);
+void nvme_update_ana(struct nvme_ns *ns, u16 status);
void nvme_kick_requeue_lists(struct nvme_ctrl *ctrl);
int nvme_mpath_alloc_disk(struct nvme_ctrl *ctrl,struct nvme_ns_head *head);
void nvme_mpath_add_disk(struct nvme_ns *ns, struct nvme_id_ns *id);
@@ -507,6 +508,9 @@ static inline void nvme_set_disk_name(char *disk_name, struct nvme_ns *ns,
static inline void nvme_failover_req(struct request *req)
{
}
+static inline void nvme_update_ana(struct nvme_ns *ns, u16 status)
+{
+}
static inline void nvme_kick_requeue_lists(struct nvme_ctrl *ctrl)
{
}
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