3 files changed, 105 insertions, 2 deletions

diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
index 23b3c7e79d4..7e26fb3c275 100644
--- a/drivers/usb/core/driver.c
+++ b/drivers/usb/core/driver.c
@@ -184,6 +184,20 @@ static int usb_unbind_device(struct device *dev)
 	return 0;
 }
 
+/*
+ * Cancel any pending scheduled resets
+ *
+ * [see usb_queue_reset_device()]
+ *
+ * Called after unconfiguring / when releasing interfaces. See
+ * comments in __usb_queue_reset_device() regarding
+ * udev->reset_running.
+ */
+static void usb_cancel_queued_reset(struct usb_interface *iface)
+{
+	if (iface->reset_running == 0)
+		cancel_work_sync(&iface->reset_ws);
+}
 
 /* called from driver core with dev locked */
 static int usb_probe_interface(struct device *dev)
@@ -242,6 +256,7 @@ static int usb_probe_interface(struct device *dev)
 			mark_quiesced(intf);
 			intf->needs_remote_wakeup = 0;
 			intf->condition = USB_INTERFACE_UNBOUND;
+			usb_cancel_queued_reset(intf);
 		} else
 			intf->condition = USB_INTERFACE_BOUND;
 
@@ -272,6 +287,7 @@ static int usb_unbind_interface(struct device *dev)
 		usb_disable_interface(udev, intf);
 
 	driver->disconnect(intf);
+	usb_cancel_queued_reset(intf);
 
 	/* Reset other interface state.
 	 * We cannot do a Set-Interface if the device is suspended or
@@ -380,8 +396,10 @@ void usb_driver_release_interface(struct usb_driver *driver,
 	if (device_is_registered(dev)) {
 		iface->condition = USB_INTERFACE_UNBINDING;
 		device_release_driver(dev);
+	} else {
+		iface->condition = USB_INTERFACE_UNBOUND;
+		usb_cancel_queued_reset(iface);
 	}
-
 	dev->driver = NULL;
 	usb_set_intfdata(iface, NULL);
 
@@ -942,7 +960,8 @@ static int usb_suspend_interface(struct usb_device *udev,
 	if (udev->state == USB_STATE_NOTATTACHED || !is_active(intf))
 		goto done;
 
-	if (intf->condition == USB_INTERFACE_UNBOUND)	/* This can't happen */
+	/* This can happen; see usb_driver_release_interface() */
+	if (intf->condition == USB_INTERFACE_UNBOUND)
 		goto done;
 	driver = to_usb_driver(intf->dev.driver);
 
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 95fb3104ba4..e65881899c8 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -3518,3 +3518,46 @@ int usb_reset_device(struct usb_device *udev)
 	return ret;
 }
 EXPORT_SYMBOL_GPL(usb_reset_device);
+
+
+/**
+ * usb_queue_reset_device - Reset a USB device from an atomic context
+ * @iface: USB interface belonging to the device to reset
+ *
+ * This function can be used to reset a USB device from an atomic
+ * context, where usb_reset_device() won't work (as it blocks).
+ *
+ * Doing a reset via this method is functionally equivalent to calling
+ * usb_reset_device(), except for the fact that it is delayed to a
+ * workqueue. This means that any drivers bound to other interfaces
+ * might be unbound, as well as users from usbfs in user space.
+ *
+ * Corner cases:
+ *
+ * - Scheduling two resets at the same time from two different drivers
+ *   attached to two different interfaces of the same device is
+ *   possible; depending on how the driver attached to each interface
+ *   handles ->pre_reset(), the second reset might happen or not.
+ *
+ * - If a driver is unbound and it had a pending reset, the reset will
+ *   be cancelled.
+ *
+ * - This function can be called during .probe() or .disconnect()
+ *   times. On return from .disconnect(), any pending resets will be
+ *   cancelled.
+ *
+ * There is no no need to lock/unlock the @reset_ws as schedule_work()
+ * does its own.
+ *
+ * NOTE: We don't do any reference count tracking because it is not
+ *     needed. The lifecycle of the work_struct is tied to the
+ *     usb_interface. Before destroying the interface we cancel the
+ *     work_struct, so the fact that work_struct is queued and or
+ *     running means the interface (and thus, the device) exist and
+ *     are referenced.
+ */
+void usb_queue_reset_device(struct usb_interface *iface)
+{
+	schedule_work(&iface->reset_ws);
+}
+EXPORT_SYMBOL_GPL(usb_queue_reset_device);
diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
index cc47d36798b..aadf29f09c4 100644
--- a/drivers/usb/core/message.c
+++ b/drivers/usb/core/message.c
@@ -1441,6 +1441,46 @@ static struct usb_interface_assoc_descriptor *find_iad(struct usb_device *dev,
 	return retval;
 }
 
+
+/*
+ * Internal function to queue a device reset
+ *
+ * This is initialized into the workstruct in 'struct
+ * usb_device->reset_ws' that is launched by
+ * message.c:usb_set_configuration() when initializing each 'struct
+ * usb_interface'.
+ *
+ * It is safe to get the USB device without reference counts because
+ * the life cycle of @iface is bound to the life cycle of @udev. Then,
+ * this function will be ran only if @iface is alive (and before
+ * freeing it any scheduled instances of it will have been cancelled).
+ *
+ * We need to set a flag (usb_dev->reset_running) because when we call
+ * the reset, the interfaces might be unbound. The current interface
+ * cannot try to remove the queued work as it would cause a deadlock
+ * (you cannot remove your work from within your executing
+ * workqueue). This flag lets it know, so that
+ * usb_cancel_queued_reset() doesn't try to do it.
+ *
+ * See usb_queue_reset_device() for more details
+ */
+void __usb_queue_reset_device(struct work_struct *ws)
+{
+	int rc;
+	struct usb_interface *iface =
+		container_of(ws, struct usb_interface, reset_ws);
+	struct usb_device *udev = interface_to_usbdev(iface);
+
+	rc = usb_lock_device_for_reset(udev, iface);
+	if (rc >= 0) {
+		iface->reset_running = 1;
+		usb_reset_device(udev);
+		iface->reset_running = 0;
+		usb_unlock_device(udev);
+	}
+}
+
+
 /*
  * usb_set_configuration - Makes a particular device setting be current
  * @dev: the device whose configuration is being updated
@@ -1611,6 +1651,7 @@ free_interfaces:
 		intf->dev.type = &usb_if_device_type;
 		intf->dev.groups = usb_interface_groups;
 		intf->dev.dma_mask = dev->dev.dma_mask;
+		INIT_WORK(&intf->reset_ws, __usb_queue_reset_device);
 		device_initialize(&intf->dev);
 		mark_quiesced(intf);
 		dev_set_name(&intf->dev, "%d-%s:%d.%d",