nvme-mpath: fix last path removal during traffic

In case our last path is removed during traffic, we can end up requeueing
the bio(s) but never schedule the actual requeue work as upper layers
still have open handles on the mpath device node.

Fix this by scheduling requeue work if the namespace being removed is
the last path in the ns_head path list.

Fixes: 32acab3181c7 ("nvme: implement multipath access to nvme subsystems")
Signed-off-by: Sagi Grimberg <[e-mail]>
Signed-off-by: Christoph Hellwig <[e-mail]>

drivers/nvme/host/core.c

···
 	mutex_unlock(&ns->ctrl->namespaces_mutex);
 
 	synchronize_srcu(&ns->head->srcu);
+	nvme_mpath_check_last_path(ns);
 	nvme_put_ns(ns);
 }
 

drivers/nvme/host/nvme.h

···
 		rcu_assign_pointer(head->current_path, NULL);
 }
 struct nvme_ns *nvme_find_path(struct nvme_ns_head *head);
+
+static inline void nvme_mpath_check_last_path(struct nvme_ns *ns)
+{
+	struct nvme_ns_head *head = ns->head;
+
+	if (head->disk && list_empty(&head->list))
+		kblockd_schedule_work(&head->requeue_work);
+}
+
 #else
 static inline void nvme_failover_req(struct request *req)
 {
···
 {
 }
 static inline void nvme_mpath_clear_current_path(struct nvme_ns *ns)
+{
+}
+static inline void nvme_mpath_check_last_path(struct nvme_ns *ns)
 {
 }
 #endif /* CONFIG_NVME_MULTIPATH */