On Mon, Jan 27, 2025 at 03:07:15PM -0800, Elson Roy Serrao wrote:
> The role switch registration and set_role() can happen in parallel as they
> are invoked independent of each other. There is a possibility that a driver
> might spend significant amount of time in usb_role_switch_register() API
> due to the presence of time intensive operations like component_add()
> which operate under common mutex. This leads to a time window after
> allocating the switch and before setting the registered flag where the set
> role notifications are dropped. Below timeline summarizes this behavior
>
> Thread1 | Thread2
> usb_role_switch_register() |
> | |
> ---> allocate switch |
> | |
> ---> component_add() | usb_role_switch_set_role()
> | | |
> | | --> Drop role notifications
> | | since sw->registered
> | | flag is not set.
> | |
> --->Set registered flag.|
>
> To avoid this, cache the last role received and set it once the switch
> registration is complete. Since we are now caching the roles based on
> registered flag, protect this flag with the switch mutex.
Instead, why not just mark the switch registered from the get-go?
diff --git a/drivers/usb/roles/class.c b/drivers/usb/roles/class.c
index c58a12c147f4..cf38be82d397 100644
--- a/drivers/usb/roles/class.c
+++ b/drivers/usb/roles/class.c
@@ -387,6 +387,8 @@ usb_role_switch_register(struct device *parent,
dev_set_name(&sw->dev, "%s-role-switch",
desc->name ? desc->name : dev_name(parent));
+ sw->registered = true;
+
ret = device_register(&sw->dev);
if (ret) {
put_device(&sw->dev);
@@ -399,8 +401,6 @@ usb_role_switch_register(struct device *parent,
dev_warn(&sw->dev, "failed to add component\n");
}
- sw->registered = true;
-
/* TODO: Symlinks for the host port and the device controller. */
return sw;
thanks,
--
heikki
