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Re: [PATCH] hid: usbhid: fix possible deadlock in __usbhid_submit_report

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Am Dienstag, 24. April 2012, 17:46:41 schrieb Ming Lei:
> On Tue, Apr 24, 2012 at 10:22 PM, Oliver Neukum <oneukum@xxxxxxx> wrote:
> > Am Dienstag, 24. April 2012, 06:19:00 schrieb Ming Lei:
> >
> >> @@ -486,11 +494,15 @@ static void hid_ctrl(struct urb *urb)
> >>
> >>       if (usbhid->ctrlhead != usbhid->ctrltail && !hid_submit_ctrl(hid)) {
> >>               /* Successfully submitted next urb in queue */
> >> +             if (status != -ECONNRESET)
> >> +                     spin_unlock(&usbhid->unlink_lock);
> >>               spin_unlock(&usbhid->lock);
> >>               return;
> >>       }
> >>
> >>       clear_bit(HID_CTRL_RUNNING, &usbhid->iofl);
> >> +     if (status != -ECONNRESET)
> >> +             spin_unlock(&usbhid->unlink_lock);
> >>       spin_unlock(&usbhid->lock);
> >>       usb_autopm_put_interface_async(usbhid->intf);
> >>       wake_up(&usbhid->wait);
> >
> > Now you race against a double time out
> >
> > CPU A                                                           CPU B
> >
> > __usbhid_submit_report()
> > time_after()
> > usb_unlink_urb()
> > -- this has to go to the hardware -->
> >                                                                        hid_irq_out()
> >                                                                        if (status != -ECONNRESET)
> >                                                                        --> no lock
> >                                                                        hid_submit_out()
> > __usbhid_submit_report()
> > time_after()
> >                                                                        usb_submit_urb()
> 
> This submit won't happen because HID_OUT_RUNNING is not cleared.

I may be dense, but as far as I can tell a resubmit will happen, exactly if
HID_OUT_RUNNING is _not_ cleared.

	Regards
		Oliver

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