On Mon, 1 Oct 2012, Alan Stern wrote: > On Mon, 1 Oct 2012, Octavian Purdila wrote: > > > There is a race condition in the USB hub code with regard to handling > > TT clear requests that can get the HCD driver in a deadlock. Usually > > when an TT clear request is scheduled it will be executed immediately: > > > However, if a suspend operation is triggered before hub_tt_work is > > scheduled, hub_quiesce will cancel the work without notifying the HCD > > driver: > > Ah, this is a very good point. > > > When the device will resume the EHCI driver will get stuck in > > ehci_endpoint_disable waiting for the tt_clearing flag to reset: > > > This patch notifies the HCD driver via clear_tt_buffer_complete > > when canceling TT clear work so that the EHCI driver has a chance to > > clear its tt_clearing flag. > > But I don't like the proposed fix. What we really need to do is avoid > suspending the device until the clear-tt-buffer operation is complete. > Can you write a patch to do that instead? Actually, it would be sufficient to avoid suspending the _hub_ until the clear-tt-buffer operation is complete. In short, hub_quiesce() should wait until all pending TT operations have finished. The cancel_work_sync() call should be replaced with flush_work_sync(). Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
