usb: gadget: udc: core: Offload usb_udc_vbus_handler processing

usb_udc_vbus_handler() can be invoked from interrupt context by irq
handlers of the gadget drivers, however, usb_udc_connect_control() has
to run in non-atomic context due to the following:
a. Some of the gadget driver implementations expect the ->pullup
   callback to be invoked in non-atomic context.
b. usb_gadget_disconnect() acquires udc_lock which is a mutex.

Hence offload invocation of usb_udc_connect_control()
to workqueue.

UDC should not be pulled up unless gadget driver is bound. The new flag
"allow_connect" is now set by gadget_bind_driver() and cleared by
gadget_unbind_driver(). This prevents work item to pull up the gadget
even if queued when the gadget driver is already unbound.

Cc: stable@vger.kernel.org
Fixes: 1016fc0 ("USB: gadget: Fix obscure lockdep violation for udc_mutex")
Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
Reviewed-by: Alan Stern <stern@rowland.harvard.edu>
Message-ID: <20230609010227.978661-1-badhri@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/udc/core.c

@@ -37,6 +37,9 @@ static const struct bus_type gadget_bus_type;
  * @vbus: for udcs who care about vbus status, this value is real vbus status;
  * for udcs who do not care about vbus status, this value is always true
  * @started: the UDC's started state. True if the UDC had started.
+ * @allow_connect: Indicates whether UDC is allowed to be pulled up.
+ * Set/cleared by gadget_(un)bind_driver() after gadget driver is bound or
+ * unbound.
  *
  * This represents the internal data structure which is used by the UDC-class
  * to hold information about udc driver and gadget together.
@@ -48,6 +51,8 @@ struct usb_udc {
 	struct list_head		list;
 	bool				vbus;
 	bool				started;
+	bool				allow_connect;
+	struct work_struct		vbus_work;
 };
 
 static struct class *udc_class;
@@ -706,7 +711,7 @@ int usb_gadget_connect(struct usb_gadget *gadget)
 		goto out;
 	}
 
-	if (gadget->deactivated) {
+	if (gadget->deactivated || !gadget->udc->allow_connect) {
 		/*
 		 * If gadget is deactivated we only save new state.
 		 * Gadget will be connected automatically after activation.
@@ -1086,6 +1091,13 @@ static void usb_udc_connect_control(struct usb_udc *udc)
 		usb_gadget_disconnect(udc->gadget);
 }
 
+static void vbus_event_work(struct work_struct *work)
+{
+	struct usb_udc *udc = container_of(work, struct usb_udc, vbus_work);
+
+	usb_udc_connect_control(udc);
+}
+
 /**
  * usb_udc_vbus_handler - updates the udc core vbus status, and try to
  * connect or disconnect gadget
@@ -1094,14 +1106,22 @@ static void usb_udc_connect_control(struct usb_udc *udc)
  *
  * The udc driver calls it when it wants to connect or disconnect gadget
  * according to vbus status.
+ *
+ * This function can be invoked from interrupt context by irq handlers of
+ * the gadget drivers, however, usb_udc_connect_control() has to run in
+ * non-atomic context due to the following:
+ * a. Some of the gadget driver implementations expect the ->pullup
+ * callback to be invoked in non-atomic context.
+ * b. usb_gadget_disconnect() acquires udc_lock which is a mutex.
+ * Hence offload invocation of usb_udc_connect_control() to workqueue.
  */
 void usb_udc_vbus_handler(struct usb_gadget *gadget, bool status)
 {
 	struct usb_udc *udc = gadget->udc;
 
 	if (udc) {
 		udc->vbus = status;
-		usb_udc_connect_control(udc);
+		schedule_work(&udc->vbus_work);
 	}
 }
 EXPORT_SYMBOL_GPL(usb_udc_vbus_handler);
@@ -1328,6 +1348,7 @@ int usb_add_gadget(struct usb_gadget *gadget)
 	mutex_lock(&udc_lock);
 	list_add_tail(&udc->list, &udc_list);
 	mutex_unlock(&udc_lock);
+	INIT_WORK(&udc->vbus_work, vbus_event_work);
 
 	ret = device_add(&udc->dev);
 	if (ret)
@@ -1459,6 +1480,7 @@ void usb_del_gadget(struct usb_gadget *gadget)
 	flush_work(&gadget->work);
 	device_del(&gadget->dev);
 	ida_free(&gadget_id_numbers, gadget->id_number);
+	cancel_work_sync(&udc->vbus_work);
 	device_unregister(&udc->dev);
 }
 EXPORT_SYMBOL_GPL(usb_del_gadget);
@@ -1527,6 +1549,7 @@ static int gadget_bind_driver(struct device *dev)
 	if (ret)
 		goto err_start;
 	usb_gadget_enable_async_callbacks(udc);
+	udc->allow_connect = true;
 	usb_udc_connect_control(udc);
 
 	kobject_uevent(&udc->dev.kobj, KOBJ_CHANGE);
@@ -1558,6 +1581,8 @@ static void gadget_unbind_driver(struct device *dev)
 
 	kobject_uevent(&udc->dev.kobj, KOBJ_CHANGE);
 
+	udc->allow_connect = false;
+	cancel_work_sync(&udc->vbus_work);
 	usb_gadget_disconnect(gadget);
 	usb_gadget_disable_async_callbacks(udc);
 	if (gadget->irq)