[PATCH] nvmet: fix the Oops in the tracing for flush cmd

[Christoph Hellwig]

I think the problem is that the extra namespace lookup doesn't make
sense to start with.  We'll need to reuse req->ns, and for that move
the init tracepoint a bit:

diff --git a/drivers/nvme/target/core.c b/drivers/nvme/target/core.c
index aafcbc424b7a94..6b610b68c44226 100644
--- a/drivers/nvme/target/core.c
+++ b/drivers/nvme/target/core.c
@@ -907,8 +907,6 @@ bool nvmet_req_init(struct nvmet_req *req, struct nvmet_cq *cq,
 	req->error_loc = NVMET_NO_ERROR_LOC;
 	req->error_slba = 0;
 
-	trace_nvmet_req_init(req, req->cmd);
-
 	/* no support for fused commands yet */
 	if (unlikely(flags & (NVME_CMD_FUSE_FIRST | NVME_CMD_FUSE_SECOND))) {
 		req->error_loc = offsetof(struct nvme_common_command, flags);
@@ -937,6 +935,8 @@ bool nvmet_req_init(struct nvmet_req *req, struct nvmet_cq *cq,
 
 	if (status)
 		goto fail;
+	
+	trace_nvmet_req_init(req, req->cmd);
 
 	if (unlikely(!percpu_ref_tryget_live(&sq->ref))) {
 		status = NVME_SC_INVALID_FIELD | NVME_SC_DNR;
diff --git a/drivers/nvme/target/trace.h b/drivers/nvme/target/trace.h
index 0458046d650178..c14e3249a14dc8 100644
--- a/drivers/nvme/target/trace.h
+++ b/drivers/nvme/target/trace.h
@@ -46,19 +46,12 @@ static inline struct nvmet_ctrl *nvmet_req_to_ctrl(struct nvmet_req *req)
 	return req->sq->ctrl;
 }
 
-static inline void __assign_disk_name(char *name, struct nvmet_req *req,
-		bool init)
+static inline void __assign_req_name(char *name, struct nvmet_req *req)
 {
-	struct nvmet_ctrl *ctrl = nvmet_req_to_ctrl(req);
-	struct nvmet_ns *ns;
-
-	if ((init && req->sq->qid) || (!init && req->cq->qid)) {
-		ns = nvmet_find_namespace(ctrl, req->cmd->rw.nsid);
-		strncpy(name, ns->device_path, DISK_NAME_LEN);
-		return;
-	}
-
-	memset(name, 0, DISK_NAME_LEN);
+	if (req->ns)
+		strncpy(name, req->ns->device_path, DISK_NAME_LEN);
+	else
+		memset(name, 0, DISK_NAME_LEN);
 }
 #endif
 
@@ -81,7 +74,7 @@ TRACE_EVENT(nvmet_req_init,
 	TP_fast_assign(
 		__entry->cmd = cmd;
 		__entry->ctrl = nvmet_req_to_ctrl(req);
-		__assign_disk_name(__entry->disk, req, true);
+		__assign_req_name(__entry->disk, req);
 		__entry->qid = req->sq->qid;
 		__entry->cid = cmd->common.command_id;
 		__entry->opcode = cmd->common.opcode;
@@ -121,7 +114,7 @@ TRACE_EVENT(nvmet_req_complete,
 		__entry->cid = req->cqe->command_id;
 		__entry->result = le64_to_cpu(req->cqe->result.u64);
 		__entry->status = le16_to_cpu(req->cqe->status) >> 1;
-		__assign_disk_name(__entry->disk, req, false);
+		__assign_req_name(__entry->disk, req);
 	),
 	TP_printk("nvmet%s: %sqid=%d, cmdid=%u, res=%#llx, status=%#x",
 		__print_ctrl_name(__entry->ctrl),