USB: Introduce usb_queue_reset() to do resets from atomic contexts

This patch introduces a new call to be able to do a USB reset from an
atomic contect. This is quite helpful in USB callbacks to handle
errors (when the only thing that can be done is to do a device
reset).

It is done queuing a work struct that will do the actual reset. The
struct is "attached" to an interface so pending requests from an
interface are removed when said interface is unbound from the driver.

The call flow then becomes:

usb_queue_reset_device()
  __usb_queue_reset_device() [workqueue]
    usb_reset_device()

usb_probe_interface()
  usb_cancel_queue_reset()      [error path]

usb_unbind_interface()
  usb_cancel_queue_reset()

usb_driver_release_interface()
  usb_cancel_queue_reset()

Note usb_cancel_queue_reset() needs smarts to try not to unqueue when
it is actually being executed. This happens when we run the reset from
the workqueue: usb_reset_device() is called and on interface unbind
time, usb_cancel_queue_reset() would be called. That would deadlock on
cancel_work_sync(). To avoid that, we set (before running
usb_reset_device()) usb_intf->reset_running and clear it inmediately
after returning.

Patch is against 2.6.28-rc2 and depends on
http://marc.info/?l=linux-usb&m=122581634925308&w=2 (as submitted by
Alan Stern).

Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 21 insertions, 2 deletions

diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
index 23b3c7e..7e26fb3 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);