On Sun, 24 Aug 2014, vichy wrote:
> hi Alan:
> >
> > I originally tried using usb_reset_device, and it caused a deadlock:
> >
> > Unplug the HID device.
> >
> > I/O error occurs. hid_io_error schedules reset_work.
> >
> > The reset_work callback routine is hid_reset. It calls
> > usb_reset_device.
> >
> > The reset fails because the device is gone. At the end of the
> > reset, hid_post_reset is called.
> >
> > hid_post_reset returns 1 because hid_get_class_descriptor
> > fails.
> >
> > Because the post_reset routine failed, usb_reset_device calls
> > usb_unbind_and_rebind_marked_interfaces.
>
> "usb_unbind_and_rebind_marked_interfaces" is called if config
> parameter is not null,
> it seems no matter post_reset routine fail or not.
Yes, that's right. I should have said: "Because the post_reset routine
failed, usb_unbind_and_rebind_marked_interfaces indirectly calls
usbhid_disconnect.
> > That routine indirectly calls usbhid_disconnect.
>
> Why that routine, usb_reset_device, will call usbhid_disconnect?
> No matter port reset success or fail, usbhid_disconnect should not be
> called except that did happen disconnection.
usbhid_disconnect gets called when the driver is unbound, regardless of
whether the device was unplugged. The kernel unbinds a driver when a
device is reset but the driver isn't able to handle the reset.
> > usbhid_disconnect calls usbhid_close by way of
> > hid_destroy_device.
>
> below is the content of hid_destroy and hid_remove_device, but I
> cannot find where usbhid_close be called by way of hid_destroy_device.
> static void hid_remove_device(struct hid_device *hdev)
> {
> if (hdev->status & HID_STAT_ADDED) {
> device_del(&hdev->dev);
> hid_debug_unregister(hdev);
> hdev->status &= ~HID_STAT_ADDED;
> }
> kfree(hdev->dev_rdesc);
> hdev->dev_rdesc = NULL;
> hdev->dev_rsize = 0;
> }
>
> void hid_destroy_device(struct hid_device *hdev)
> {
> hid_remove_device(hdev);
> put_device(&hdev->dev);
> }
I don't remember the entire call chain. It was pretty long.
hid_destroy_device calls hid_remove_device, which calls device_del,
which calls lots of other things. If you really want to see all the
details, put a dump_stack() call in usbhid_close and examine what it
prints in the kernel log when you unplug an HID device.
Alan Stern
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