On Sun, Apr 22, 2012 at 8:50 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > On Sun, 22 Apr 2012, Ming Lei wrote: > >> > Although the kerneldoc doesn't actually say so, it should be safe to >> > assume that usb_unlink_urb calls the completion routine directly _only_ >> > in cases where the unlink succeeded. (We could add this to the >> > kerneldoc.) >> > >> > Therefore: If the URB completes with status other than -ECONNRESET then >> > you can safely take the lock for resubmission. If the URB completes >> > with status == -ECONNRESET then you know it was unlinked, so you don't >> > need to take the lock -- the race has already been lost. >> > >> > Does that solve your problem? >> >> Not sure if that does work. >> >> If the URB completes asynchronously after unlinking, its status is still >> -ECONNRESET, so extra race may be caused without holding the lock >> because complete handler will access some global data. > > That would be a completely separate race, right? So maybe it can use a Not sure, at least in both usbnet and usbhid cases, the lock is held before usb_unlink_urb, and the same lock is to be acquired in the URB complete handler. > different lock for protection -- and this other lock could be dropped > before usb_unlink_urb is called. If the lock which is to be acquired in the URB complete handler is dropped before calling usb_unlink_urb, one new submitted URB in complete handler may be unlinked, as mentioned by Oliver already. Thanks, -- Ming Lei -- 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
