nvmet: protect discovery change log event list iteration

When we iterate on the discovery subsystem controllers
we need to protect against concurrent mutations to it.

Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Minwoo Im <minwoo.im@samsung.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/target/discovery.c

@@ -30,14 +30,17 @@ void nvmet_port_disc_changed(struct nvmet_port *port,
 {
 	struct nvmet_ctrl *ctrl;
 
+	lockdep_assert_held(&nvmet_config_sem);
 	nvmet_genctr++;
 
+	mutex_lock(&nvmet_disc_subsys->lock);
 	list_for_each_entry(ctrl, &nvmet_disc_subsys->ctrls, subsys_entry) {
 		if (subsys && !nvmet_host_allowed(subsys, ctrl->hostnqn))
 			continue;
 
 		__nvmet_disc_changed(port, ctrl);
 	}
+	mutex_unlock(&nvmet_disc_subsys->lock);
 }
 
 static void __nvmet_subsys_disc_changed(struct nvmet_port *port,
@@ -46,12 +49,14 @@ static void __nvmet_subsys_disc_changed(struct nvmet_port *port,
 {
 	struct nvmet_ctrl *ctrl;
 
+	mutex_lock(&nvmet_disc_subsys->lock);
 	list_for_each_entry(ctrl, &nvmet_disc_subsys->ctrls, subsys_entry) {
 		if (host && strcmp(nvmet_host_name(host), ctrl->hostnqn))
 			continue;
 
 		__nvmet_disc_changed(port, ctrl);
 	}
+	mutex_unlock(&nvmet_disc_subsys->lock);
 }
 
 void nvmet_subsys_disc_changed(struct nvmet_subsys *subsys,