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.

Reported by:	Mike_Karels@mcafee.com
MFC after:	1 week

1 files changed, 32 insertions, 2 deletions

diff --git a/sys/dev/usb/input/ukbd.c b/sys/dev/usb/input/ukbd.c
index aa68f7e..1ad3bd5 100644
--- a/sys/dev/usb/input/ukbd.c
+++ b/sys/dev/usb/input/ukbd.c
@@ -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, uint32_t key)
 }
 
 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, uint8_t wait)
 
 	if (kdb_active == 0) {
 		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)