Index: sys/arm/at91/at91_rst.c
===================================================================
--- sys/arm/at91/at91_rst.c
+++ sys/arm/at91/at91_rst.c
@@ -124,7 +124,7 @@
 	at91_rst_sc = sc = device_get_softc(dev);
 	sc->sc_dev = dev;
 
-	callout_init(&sc->tick_ch, 0);
+	callout_init(&sc->tick_ch, 1);
 
 	rid = 0;
 	sc->mem_res = bus_alloc_resource_any(dev, SYS_RES_MEMORY, &rid,
Index: sys/dev/syscons/syscons.c
===================================================================
--- sys/dev/syscons/syscons.c
+++ sys/dev/syscons/syscons.c
@@ -3858,22 +3858,28 @@
 
 	    case RBT:
 #ifndef SC_DISABLE_REBOOT
-		if (enable_reboot && !(flags & SCGETC_CN))
+		if (enable_reboot && !(flags & SCGETC_CN)) {
+			mtx_unlock(&Giant);
 			shutdown_nice(0);
+		}
 #endif
 		break;
 
 	    case HALT:
 #ifndef SC_DISABLE_REBOOT
-		if (enable_reboot && !(flags & SCGETC_CN))
+		if (enable_reboot && !(flags & SCGETC_CN)) {
+			mtx_unlock(&Giant);
 			shutdown_nice(RB_HALT);
+		}
 #endif
 		break;
 
 	    case PDWN:
 #ifndef SC_DISABLE_REBOOT
-		if (enable_reboot && !(flags & SCGETC_CN))
+		if (enable_reboot && !(flags & SCGETC_CN)) {
+			mtx_unlock(&Giant);
 			shutdown_nice(RB_HALT|RB_POWEROFF);
+		}
 #endif
 		break;
 
Index: sys/kern/init_main.c
===================================================================
--- sys/kern/init_main.c
+++ sys/kern/init_main.c
@@ -703,10 +703,6 @@
 	struct thread *td;
 	struct proc *p;
 
-	mtx_lock(&Giant);
-
-	GIANT_REQUIRED;
-
 	TSENTER();	/* Here so we don't overlap with mi_startup. */
 
 	td = curthread;
@@ -801,7 +797,6 @@
 		 * to user mode as init!
 		 */
 		if ((error = sys_execve(td, &args)) == EJUSTRETURN) {
-			mtx_unlock(&Giant);
 			TSEXIT();
 			return;
 		}
Index: sys/kern/kern_shutdown.c
===================================================================
--- sys/kern/kern_shutdown.c
+++ sys/kern/kern_shutdown.c
@@ -268,13 +268,10 @@
 	if (error == 0)
 		error = priv_check(td, PRIV_REBOOT);
 	if (error == 0) {
-		if (uap->opt & RB_REROOT) {
+		if (uap->opt & RB_REROOT)
 			error = kern_reroot();
-		} else {
-			mtx_lock(&Giant);
+		else
 			kern_reboot(uap->opt);
-			mtx_unlock(&Giant);
-		}
 	}
 	return (error);
 }
Index: sys/kern/vfs_bio.c
===================================================================
--- sys/kern/vfs_bio.c
+++ sys/kern/vfs_bio.c
@@ -1240,25 +1240,20 @@
 
 #ifdef PREEMPTION
 		/*
-		 * Drop Giant and spin for a while to allow
-		 * interrupt threads to run.
+		 * Spin for a while to allow interrupt threads to run.
 		 */
-		DROP_GIANT();
 		DELAY(50000 * iter);
-		PICKUP_GIANT();
 #else
 		/*
-		 * Drop Giant and context switch several times to
-		 * allow interrupt threads to run.
+		 * Context switch several times to allow interrupt
+		 * threads to run.
 		 */
-		DROP_GIANT();
 		for (subiter = 0; subiter < 50 * iter; subiter++) {
 			thread_lock(curthread);
 			mi_switch(SW_VOL, NULL);
 			thread_unlock(curthread);
 			DELAY(1000);
 		}
-		PICKUP_GIANT();
 #endif
 	}
 	printf("\n");
Index: sys/kern/vfs_mountroot.c
===================================================================
--- sys/kern/vfs_mountroot.c
+++ sys/kern/vfs_mountroot.c
@@ -579,9 +579,7 @@
 
 	if (root_mount_mddev != -1) {
 		mdio->md_unit = root_mount_mddev;
-		DROP_GIANT();
 		error = kern_ioctl(td, fd, MDIOCDETACH, (void *)mdio);
-		PICKUP_GIANT();
 		/* Ignore errors. We don't care. */
 		root_mount_mddev = -1;
 	}
@@ -590,9 +588,7 @@
 	mdio->md_options = MD_AUTOUNIT | MD_READONLY;
 	mdio->md_mediasize = sb.st_size;
 	mdio->md_unit = 0;
-	DROP_GIANT();
 	error = kern_ioctl(td, fd, MDIOCATTACH, (void *)mdio);
-	PICKUP_GIANT();
 	if (error)
 		goto out;
 
@@ -601,9 +597,7 @@
 		mdio->md_file = NULL;
 		mdio->md_options = 0;
 		mdio->md_mediasize = 0;
-		DROP_GIANT();
 		error = kern_ioctl(td, fd, MDIOCDETACH, (void *)mdio);
-		PICKUP_GIANT();
 		/* Ignore errors. We don't care. */
 		error = ERANGE;
 		goto out;
@@ -960,9 +954,7 @@
 
 	curfail = 0;
 	while (1) {
-		DROP_GIANT();
 		g_waitidle();
-		PICKUP_GIANT();
 		mtx_lock(&root_holds_mtx);
 		if (LIST_EMPTY(&root_holds)) {
 			mtx_unlock(&root_holds_mtx);
@@ -1004,9 +996,7 @@
 	 * Note that we must wait for GEOM to finish reconfiguring itself,
 	 * eg for geom_part(4) to finish tasting.
 	 */
-	DROP_GIANT();
 	g_waitidle();
-	PICKUP_GIANT();
 	if (parse_mount_dev_present(dev))
 		return (0);
 
@@ -1038,6 +1028,8 @@
 	time_t timebase;
 	int error;
 	
+	mtx_assert(&Giant, MA_NOTOWNED);
+
 	TSENTER();
 
 	td = curthread;
Index: sys/sparc64/pci/psycho.c
===================================================================
--- sys/sparc64/pci/psycho.c
+++ sys/sparc64/pci/psycho.c
@@ -810,6 +810,7 @@
 		return;
 	shutdown++;
 	printf("Power Failure Detected: Shutting down NOW.\n");
+	mtx_unlock(&Giant);
 	shutdown_nice(RB_POWEROFF);
 }
 
@@ -823,6 +824,7 @@
 		return;
 	shutdown++;
 	printf("DANGER: OVER TEMPERATURE detected.\nShutting down NOW.\n");
+	mtx_unlock(&Giant);
 	shutdown_nice(RB_POWEROFF);
 }
 
Index: sys/sparc64/sbus/sbus.c
===================================================================
--- sys/sparc64/sbus/sbus.c
+++ sys/sparc64/sbus/sbus.c
@@ -411,7 +411,7 @@
 	    INTIGN(vec = rman_get_start(sc->sc_ot_ires)) != sc->sc_ign ||
 	    INTVEC(SYSIO_READ8(sc, SBR_THERM_INT_MAP)) != vec ||
 	    intr_vectors[vec].iv_ic != &sbus_ic ||
-	    bus_setup_intr(dev, sc->sc_ot_ires, INTR_TYPE_MISC | INTR_BRIDGE,
+	    bus_setup_intr(dev, sc->sc_ot_ires, INTR_TYPE_MISC | INTR_BRIDGE | INTR_MPSAFE,
 	    NULL, sbus_overtemp, sc, &sc->sc_ot_ihand) != 0)
 		panic("%s: failed to set up temperature interrupt", __func__);
 	i = 3;
@@ -421,7 +421,7 @@
 	    INTIGN(vec = rman_get_start(sc->sc_pf_ires)) != sc->sc_ign ||
 	    INTVEC(SYSIO_READ8(sc, SBR_POWER_INT_MAP)) != vec ||
 	    intr_vectors[vec].iv_ic != &sbus_ic ||
-	    bus_setup_intr(dev, sc->sc_pf_ires, INTR_TYPE_MISC | INTR_BRIDGE,
+	    bus_setup_intr(dev, sc->sc_pf_ires, INTR_TYPE_MISC | INTR_BRIDGE | INTR_MPSAFE,
 	    NULL, sbus_pwrfail, sc, &sc->sc_pf_ihand) != 0)
 		panic("%s: failed to set up power fail interrupt", __func__);