[PATCHv4] nvme: allow to re-attach namespaces after all paths are down

[Hannes Reinecke]

We should only remove the ns head from the list of heads per
subsystem if the reference count drops to zero. Removing it
at the start of nvme_ns_remove() will prevent us from reattaching
the namespace to the correct ns head once a path becomes available
again.

Changes to v3:
- Simplify if() clause to detect duplicate namespaces
Changes to v2:
- Drop memcpy() statement
Changes to v1:
- Always check NSIDs after reattach

Signed-off-by: Hannes Reinecke <hare at suse.de>
---
 drivers/nvme/host/core.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 522c9b229f80..a60144a4054a 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -546,6 +546,9 @@ static void nvme_free_ns_head(struct kref *ref)
 	struct nvme_ns_head *head =
 		container_of(ref, struct nvme_ns_head, ref);
 
+	mutex_lock(&head->subsys->lock);
+	list_del_init(&head->entry);
+	mutex_unlock(&head->subsys->lock);
 	nvme_mpath_remove_disk(head);
 	ida_simple_remove(&head->subsys->ns_ida, head->instance);
 	cleanup_srcu_struct(&head->srcu);
@@ -3605,7 +3608,11 @@ static int nvme_init_ns_head(struct nvme_ns *ns, unsigned nsid,
 		head->shared = is_shared;
 	} else {
 		ret = -EINVAL;
-		if (!is_shared || !head->shared) {
+		/*
+		 * If multipath is enabled we might hit an ns head with no
+		 * paths, but that doesn't indicate it's a shared namespace.
+		 */
+		if (!list_empty(&head->list) && (!is_shared || !head->shared)) {
 			dev_err(ctrl->device,
 				"Duplicate unshared namespace %d\n", nsid);
 			goto out_put_ns_head;
@@ -3764,8 +3771,6 @@ static void nvme_ns_remove(struct nvme_ns *ns)
 
 	mutex_lock(&ns->ctrl->subsys->lock);
 	list_del_rcu(&ns->siblings);
-	if (list_empty(&ns->head->list))
-		list_del_init(&ns->head->entry);
 	mutex_unlock(&ns->ctrl->subsys->lock);
 
 	synchronize_rcu(); /* guarantee not available in head->list */
-- 
2.29.2