On Fri, 13 Apr 2012, Steven Rostedt wrote:
> > Second, if you do
> >
> > echo 0 >/sys/bus/usb/devices/usb1/bConfigurationValue
>
> This never returned. I did the echo, and the command locked up.
>
> (process 3077)
>
> cat /proc/3077/wchan
> usb_disconnect
I found the reason for the deadlock. The patch below will work around
the problem for now, although it's not a correct fix. You'll still get
some complaints from lockdep.
Alan Stern
Index: usb-3.4/drivers/usb/core/hub.c
===================================================================
--- usb-3.4.orig/drivers/usb/core/hub.c
+++ usb-3.4/drivers/usb/core/hub.c
@@ -1667,7 +1667,7 @@ void usb_disconnect(struct usb_device **
{
struct usb_device *udev = *pdev;
int i;
- struct usb_hcd *hcd = bus_to_hcd(udev->bus);
+// struct usb_hcd *hcd = bus_to_hcd(udev->bus);
/* mark the device as inactive, so any further urb submissions for
* this device (and any of its children) will fail immediately.
@@ -1690,9 +1690,9 @@ void usb_disconnect(struct usb_device **
* so that the hardware is now fully quiesced.
*/
dev_dbg (&udev->dev, "unregistering device\n");
- mutex_lock(hcd->bandwidth_mutex);
+// mutex_lock(hcd->bandwidth_mutex);
usb_disable_device(udev, 0);
- mutex_unlock(hcd->bandwidth_mutex);
+// mutex_unlock(hcd->bandwidth_mutex);
usb_hcd_synchronize_unlinks(udev);
usb_remove_ep_devs(&udev->ep0);
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