On Sat, Apr 21, 2012 at 6:25 PM, Oliver Neukum <oliver@xxxxxxxxxx> wrote: > Am Samstag, 21. April 2012, 02:37:35 schrieb Alan Stern: >> On Fri, 20 Apr 2012, Oliver Neukum wrote: >> >> > As I said, I'd very much appreciate sane semantics for usb_unlink_urb(). >> >> Aside from the practicality issue of altering a large number of >> existing drivers, changing the semantics the way you want would be >> difficult because it would force the HCDs to defer some giveback >> operations to a bottom half or timer routine. > > Or a work queue, which would have to be dedicated to avoid deadlocks > with storage. > >> Think about what happens if the URB being unlinked hasn't been >> presented to the hardware yet. Once it has been removed from the HCD's >> internal lists, there's no reason not to give it back right away. And >> there's no natural time to give it back later. > > Now. The question is not when, but from which context. > The context should be uniform, so that the requirements > for locking should also be uniform. How about always scheduling a tasklet to run what usb_unlink_urb does? just implement usb_unlink_urb as something like tasklet_schedule(unlink_tasklet). Then we can have a uniform lock requirement and no changes are involved on host controller drivers. 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
