[PATCH] nvme: explicitly use normal NVMe error handling when appropriate

[Mike Snitzer]

On Mon, Aug 10 2020 at 10:36am -0400,
Mike Snitzer <snitzer at redhat.com> wrote:

> On Fri, Aug 07 2020 at  7:35pm -0400,
> Sagi Grimberg <sagi at grimberg.me> wrote:
> 
> > 
> > >>Hey Mike,
...
> > >I think NVMe can easily fix this by having an earlier stage of checking,
> > >e.g. nvme_local_retry_req(), that shortcircuits ever getting to
> > >higher-level multipathing consideration (be it native NVMe or DM
> > >multipathing) for cases like NVME_SC_CMD_INTERRUPTED.
> > >To be clear: the "default" case of nvme_failover_req() that returns
> > >false to fallback to NVMe's "local" normal NVMe error handling -- that
> > >can stay.. but a more explicit handling of cases like
> > >NVME_SC_CMD_INTERRUPTED should be added to a nvme_local_retry_req()
> > >check that happens before nvme_failover_req() in nvme_complete_rq().
> > 
> > I don't necessarily agree with having a dedicated nvme_local_retry_req().
> > a request that isn't failed over, goes to local error handling (retry or
> > not). I actually think that just adding the condition to
> > nvme_complete_req and having nvme_failover_req reject it would work.
> > 
> > Keith?
> 
> I think that is basically what I'm thinking too.

From: Mike Snitzer <snitzer at redhat.com>
Subject: nvme: explicitly use normal NVMe error handling when appropriate

Commit 764e9332098c0 ("nvme-multipath: do not reset on unknown
status"), among other things, fixed NVME_SC_CMD_INTERRUPTED error
handling by changing multipathing's nvme_failover_req() to short-circuit
path failover and then fallback to NVMe's normal error handling (which
takes care of NVME_SC_CMD_INTERRUPTED).

This detour through native NVMe multipathing code is unwelcome because
it prevents NVMe core from handling NVME_SC_CMD_INTERRUPTED independent
of any multipathing concerns.

Introduce nvme_status_needs_local_error_handling() to prioritize
non-failover retry, when appropriate, in terms of normal NVMe error
handling.  nvme_status_needs_local_error_handling() will naturely evolve
to include handling of any other errors that normal error handling must
be used for.

nvme_failover_req()'s ability to fallback to normal NVMe error handling
has been preserved because it may be useful for future NVME_SC that
nvme_status_needs_local_error_handling() hasn't yet been trained for.

Signed-off-by: Mike Snitzer <snitzer at redhat.com>
---
 drivers/nvme/host/core.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 88cff309d8e4..be749b690af7 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -252,6 +252,16 @@ static inline bool nvme_req_needs_retry(struct request *req)
 	return true;
 }
 
+static inline bool nvme_status_needs_local_error_handling(u16 status)
+{
+	switch (status & 0x7ff) {
+	case NVME_SC_CMD_INTERRUPTED:
+		return true;
+	default:
+		return false;
+	}
+}
+
 static void nvme_retry_req(struct request *req)
 {
 	struct nvme_ns *ns = req->q->queuedata;
@@ -270,7 +280,8 @@ static void nvme_retry_req(struct request *req)
 
 void nvme_complete_rq(struct request *req)
 {
-	blk_status_t status = nvme_error_status(nvme_req(req)->status);
+	u16 nvme_status = nvme_req(req)->status;
+	blk_status_t status = nvme_error_status(nvme_status);
 
 	trace_nvme_complete_rq(req);
 
@@ -280,7 +291,8 @@ void nvme_complete_rq(struct request *req)
 		nvme_req(req)->ctrl->comp_seen = true;
 
 	if (unlikely(status != BLK_STS_OK && nvme_req_needs_retry(req))) {
-		if ((req->cmd_flags & REQ_NVME_MPATH) && nvme_failover_req(req))
+		if (!nvme_status_needs_local_error_handling(nvme_status) &&
+		    (req->cmd_flags & REQ_NVME_MPATH) && nvme_failover_req(req))
 			return;
 
 		if (!blk_queue_dying(req->q)) {
-- 
2.18.0