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, 1 insertions, 1 deletions

diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 9a3d3540aa6a..29942b1892f7 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -141,7 +141,7 @@ struct nvme_ctrl {
 	struct blk_mq_tag_set *tagset;
 	struct blk_mq_tag_set *admin_tagset;
 	struct list_head namespaces;
-	struct mutex namespaces_mutex;
+	struct rw_semaphore namespaces_rwsem;
 	struct device ctrl_device;
 	struct device *device;	/* char device */
 	struct cdev cdev;