On Wed, 29 Aug 2012, Sebastian Andrzej Siewior wrote: > Take g_ncm for instance. It enqueues a few BULK URBs on receive side and > an INTR URB. You mean the host driver enqueues these things, not g_ncm, right? > Now we remove the g_ncm module. This starts with > usb_gadget_disconnect() which disables the UDC. Now lets say the timer > expires and dummy_timer() is invoked. It can't find a pair between the > UDC endpoint and URB's address in find_endpoint() because the > is_active() is no longer true. So we start a cleanup of URBs. > The BULK URBs usually don't make a scene. They re-submit the complete > queue length in BH so we have a little time in between. The INTR URB is > more evil because usbnet's intr_complete() causes to re-submitt it > immediately. That means we hardly do any progress and end up in a > busy loop. This sounds like a possible bug in usbnet. If usbnet encounters repeated failures while trying to communicate with a USB device, it shouldn't continue to retry indefinitely. It should eventually give up, and maybe do a device reset. > This patch changes the status code for URBs which can not be assigned to > an endpoint (because the UDC is in pulldown) are now given back with > -ESHUTDOWN. The BULK endpoints in ncm are re-submitted in batches of 10 > in BH but the INTR URB will never be re-submitted. This gives us somes > air to make some progress and remove the gadget. > > An alternative approach would be to not accept any new URBs once the > port is not active. Something similar is already done on the UDC side. I don't see why either of these changes should be needed. dummy-hcd's current behavior is the same as what you would get if you attached the gadget to an EHCI controller and then unplugged the cable. When ehci-hcd can't carry out a transfer because the device doesn't respond, it returns a -EPROTO error status for the URB. We want dummy-hcd to do the same thing. Similarly, when you unplug a device, ehci-hcd doesn't immediately stop accepting URBs for that device. We accept new URBs until the hub driver is notified about the disconnection and the device is unregistered. NAK. 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
