nvme: change namespaces_mutext to namespaces_rwsem

namespaces_mutext is used to synchronize the operations on ctrl
namespaces list. Most of the time, it is a read operation.

On the other hand, there are many interfaces in nvme core that
need this lock, such as nvme_wait_freeze, and even more interfaces
will be added. If we use mutex here, circular dependency could be
introduced easily. For example:
context A                  context B
nvme_xxx                   nvme_xxx
hold namespaces_mutext     require namespaces_mutext
sync context B

So it is better to change it from mutex to rwsem.

Reviewed-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 7283d7149baf..affd67021b6f 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -44,12 +44,12 @@ void nvme_kick_requeue_lists(struct nvme_ctrl *ctrl)
 {
 	struct nvme_ns *ns;
 
-	mutex_lock(&ctrl->namespaces_mutex);
+	down_read(&ctrl->namespaces_rwsem);
 	list_for_each_entry(ns, &ctrl->namespaces, list) {
 		if (ns->head->disk)
 			kblockd_schedule_work(&ns->head->requeue_work);
 	}
-	mutex_unlock(&ctrl->namespaces_mutex);
+	up_read(&ctrl->namespaces_rwsem);
 }
 
 static struct nvme_ns *__nvme_find_path(struct nvme_ns_head *head)