on 14/07/2011 00:07 Hans Petter Selasky said the following:
> Author: hselasky
> Date: Wed Jul 13 21:07:50 2011
> New Revision: 223989
> URL: http://svn.freebsd.org/changeset/base/223989
>
> Log:
> Fix for dump after shutdown with USB keyboard plugged in. It appears that
> the
> system timer is stopped during shutdown and that the pause() statement in
> ukbd
> causes infinite hang in this regard. The fix is to use mi_switch() instead
> of
> pause() to do the required task switch to ensure that the required USB
> processes
> get executed.
I have a question partially about this particular change, partially about
USB/ukbd
polling mode in general. See below:
> Reported by: mike_kar...@mcafee.com
> MFC after: 1 week
>
> Modified:
> head/sys/dev/usb/input/ukbd.c
>
> Modified: head/sys/dev/usb/input/ukbd.c
> ==============================================================================
> --- head/sys/dev/usb/input/ukbd.c Wed Jul 13 21:07:41 2011
> (r223988)
> +++ head/sys/dev/usb/input/ukbd.c Wed Jul 13 21:07:50 2011
> (r223989)
> @@ -59,6 +59,8 @@ __FBSDID("$FreeBSD$");
> #include <sys/callout.h>
> #include <sys/malloc.h>
> #include <sys/priv.h>
> +#include <sys/proc.h>
> +#include <sys/sched.h>
> #include <sys/kdb.h>
>
> #include <dev/usb/usb.h>
> @@ -386,6 +388,33 @@ ukbd_put_key(struct ukbd_softc *sc, uint
> }
>
> static void
> +ukbd_yield(void)
> +{
> + struct thread *td = curthread;
> + uint32_t old_prio;
> +
> + DROP_GIANT();
> +
> + thread_lock(td);
> +
> + /* get current priority */
> + old_prio = td->td_base_pri;
> +
> + /* set new priority */
> + sched_prio(td, td->td_user_pri);
> +
> + /* cause a task switch */
> + mi_switch(SW_INVOL | SWT_RELINQUISH, NULL);
> +
> + /* restore priority */
> + sched_prio(td, old_prio);
> +
> + thread_unlock(td);
> +
> + PICKUP_GIANT();
> +}
> +
> +static void
> ukbd_do_poll(struct ukbd_softc *sc, uint8_t wait)
> {
> DPRINTFN(2, "polling\n");
> @@ -396,8 +425,9 @@ ukbd_do_poll(struct ukbd_softc *sc, uint
>
> if (kdb_active == 0) {
The question is: why this special subcase is needed at all.
If I understand correctly, the polling mode is used only in some special
situations/contexts.
So why not always use the generic code (after this if-block) that does "proper"
polling? What do we win when using this special case that seems to depend on
the
scheduler?
Unfortunately I couldn't fully understand commit log of r203896.
One of the reasons I am asking about this is that soon-ish we may have changes
that disable scheduler in a context where panicstr != NULL.
> while (sc->sc_inputs == 0) {
> - /* make sure the USB code gets a chance to run */
> - pause("UKBD", 1);
> +
> + /* give USB threads a chance to run */
> + ukbd_yield();
>
> /* check if we should wait */
> if (!wait)
--
Andriy Gapon
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