On Wed, 7 May 2014, Zhuang Jin Can wrote: > A delayed status request may be queued before composite framework returns > USB_GADGET_DELAYED_STATUS, because the thread queueing the request can run > on a different core in parallel with the control request irq. > > SETUP XferComplete IRQ fsg_main_thread > ---------------------- --------------- > | | > spin_lock_irqsave(&dwc->lock) sleeping > | | > ... ... > dwc3_ep0_inspect_setup() | > | | > dwc3_ep0_delegate_req() | > | | > ... | > spin_unlock(&dwc->lock); | > | | > fsg_set_alt() ======> Signal Wakeup ====> | > | | > other gadgets->set_alt() handle exception > | | > | usb_composite_setup_continue() > | | > | spin_lock_irqsave(&dwc->lock) > | __dwc3_gadget_ep0_queue() > | delay_status is false > | spin_unlock_irqrestore(&dwc->lock) > | | > | sleeping > spin_lock(&dwc->lock); | > | | > delayed_status=true | > | | > > STATUS XferNotReady IRQ > ------------------------ > | > dwc3_ep0_xfernotready() > | > delayed_status is true, return; > > The result is the status packet will never be transferred, and > delayed_status is not cleared. > > Signed-off-by: Zhuang Jin Can <jin.can.zhuang@xxxxxxxxx> > Reported-by: Zhou Liping <liping.zhou@xxxxxxxxx> A similar problem can occur in the opposite sense: The thread queuing the delayed status request might be delayed for so long that another SETUP packet arrives from the host first. In that case, the delayed status request is a response for a stale transfer, so it must not be sent to the host. Do dwc3 and composite.c handle this case correctly? Back in the old g_file_storage driver, I addressed this issue by keeping a counter of all the setup requests. When it came time to send a delayed status response, the response would be sent only if the counter had not changed from when the original setup request was received. As far as I can see, composite.c doesn't do anything like that. 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
