[PATCH] nvme: fix (S)RCU protection of nvme_ns_head list (alternate)

[Caleb Sander <csander@purestorage.com>]

This is an alternate fix, protecting the nvme_ns_head siblings list
with both RCU and SRCU.
Use RCU in nvme_mpath_revalidate_paths(), which doesn't sleep.
And add synchronize_srcu() in nvme_ns_remove(),
since nvme_ns_head_submit_bio() protects the list with SRCU.

Signed-off-by: Caleb Sander <csander@purestorage.com>
---
 drivers/nvme/host/core.c      | 1 +
 drivers/nvme/host/multipath.c | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index da55ce45ac70..9b26d4781b32 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -4305,6 +4305,7 @@ static void nvme_ns_remove(struct nvme_ns *ns)
 
 	/* guarantee not available in head->list */
 	synchronize_rcu();
+	synchronize_srcu(&ns->head->srcu);
 
 	if (!nvme_ns_head_multipath(ns->head))
 		nvme_cdev_del(&ns->cdev, &ns->cdev_device);
diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 93e2138a8b42..6d0aea477253 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -175,10 +175,12 @@ void nvme_mpath_revalidate_paths(struct nvme_ns *ns)
 	sector_t capacity = get_capacity(head->disk);
 	int node;
 
+	rcu_read_lock();
 	list_for_each_entry_rcu(ns, &head->list, siblings) {
 		if (capacity != get_capacity(ns->disk))
 			clear_bit(NVME_NS_READY, &ns->flags);
 	}
+	rcu_read_unlock();
 
 	for_each_node(node)
 		rcu_assign_pointer(head->current_path[node], NULL);
-- 
2.25.1