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From: Hans Petter Selasky <hselasky@FreeBSD.org>
Date: Wed, 13 Jul 2011 21:07:50 +0000 (UTC)
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Subject: svn commit: r223989 - head/sys/dev/usb/input
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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.
  
  Reported by:	Mike_Karels@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) {
 		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)