diff --git a/sys/arch/amd64/amd64/locore.S b/sys/arch/amd64/amd64/locore.S
index 20e55d75d901..d36b1c3d2317 100644
--- a/sys/arch/amd64/amd64/locore.S
+++ b/sys/arch/amd64/amd64/locore.S
@@ -1,4 +1,4 @@
-/*	$NetBSD: locore.S,v 1.34 2007/12/02 21:43:11 dsl Exp $	*/
+/*	$NetBSD: locore.S,v 1.35 2007/12/03 20:21:32 ad Exp $	*/
 
 /*
  * Copyright-o-rama!
@@ -865,7 +865,8 @@ ENTRY(dumpsys)
 	ret
 
 /*
- * struct lwp *cpu_switchto(struct lwp *, struct lwp *)
+ * struct lwp *cpu_switchto(struct lwp *oldlwp, struct newlwp,
+ *			    bool returning)
  *
  *	1. if (oldlwp != NULL), save its context.
  *	2. then, restore context of newlwp.
@@ -903,6 +904,13 @@ ENTRY(cpu_switchto)
 	movq	PCB_RSP(%r14),%rsp
 	movq	PCB_RBP(%r14),%rbp
 
+	/* Set curlwp. */
+	movq	%r12,CPUVAR(CURLWP)
+
+	/* Skip the rest if returning to a pinned LWP. */
+	testb	%dl,%dl
+	jnz	4f
+
 	/* Switch TSS. Reset "task busy" flag before loading. */
 #ifdef XEN
 	movq	%r14, %rdi
@@ -914,9 +922,6 @@ ENTRY(cpu_switchto)
 	ltr	%dx
 #endif
 
-	/* Set curlwp. */
-	movq	%r12,CPUVAR(CURLWP)
-
 	/* Don't bother with the rest if switching to a system process. */
 	testl	$LW_SYSTEM,L_FLAG(%r12)
 	jnz	4f
@@ -1103,10 +1108,8 @@ syscall_return:
 	movl	CPUVAR(ILEVEL),%r8d
 	xorq	%rax,%rax
 	call	_C_LABEL(printf)
-#ifdef DDB
-	int	$3
-#endif /* DDB */
-	movl	$IPL_NONE,CPUVAR(ILEVEL)
+	movl	$IPL_NONE,%edi
+	call	_C_LABEL(spllower)
 	jmp	.Lsyscall_checkast
 4:	.asciz	"WARNING: SPL NOT LOWERED ON SYSCALL %d %d EXIT %x %x\n"
 #endif
@@ -1218,10 +1221,8 @@ iret_return:
 	movabsq	$4f, %rdi
 	xorq	%rax,%rax
 	call	_C_LABEL(printf)
-#ifdef DDB
-	int	$3
-#endif /* DDB */
-	movl	$IPL_NONE,CPUVAR(ILEVEL)
+	movl	$IPL_NONE,%edi
+	call	_C_LABEL(spllower)
 	jmp	.Losyscall_checkast
 4:	.asciz	"WARNING: SPL NOT LOWERED ON SYSCALL EXIT\n"
 #endif /* DIAGNOSTIC */
diff --git a/sys/arch/amd64/amd64/trap.c b/sys/arch/amd64/amd64/trap.c
index cacabdcff45d..ec1c91c71345 100644
--- a/sys/arch/amd64/amd64/trap.c
+++ b/sys/arch/amd64/amd64/trap.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: trap.c,v 1.39 2007/12/02 16:37:58 ad Exp $	*/
+/*	$NetBSD: trap.c,v 1.40 2007/12/03 20:21:32 ad Exp $	*/
 
 /*-
  * Copyright (c) 1998, 2000 The NetBSD Foundation, Inc.
@@ -75,7 +75,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: trap.c,v 1.39 2007/12/02 16:37:58 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: trap.c,v 1.40 2007/12/03 20:21:32 ad Exp $");
 
 #include "opt_ddb.h"
 #include "opt_kgdb.h"
@@ -376,9 +376,7 @@ copyfault:
 		uvmexp.softs++;
 		if (l->l_flag & LP_OWEUPC) {
 			p->p_flag &= ~LP_OWEUPC;
-			KERNEL_LOCK(1, l);
 			ADDUPROF(l);
-			KERNEL_UNLOCK_LAST(l);
 		}
 		/* Allow a forced task switch. */
 		if (curcpu()->ci_want_resched)
diff --git a/sys/arch/amd64/amd64/vector.S b/sys/arch/amd64/amd64/vector.S
index 146304dc05d3..18e6c4c25588 100644
--- a/sys/arch/amd64/amd64/vector.S
+++ b/sys/arch/amd64/amd64/vector.S
@@ -1,4 +1,4 @@
-/*	$NetBSD: vector.S,v 1.16 2007/12/03 15:33:10 ad Exp $	*/
+/*	$NetBSD: vector.S,v 1.17 2007/12/03 20:21:33 ad Exp $	*/
 
 /*
  * Copyright (c) 2001 Wasabi Systems, Inc.
@@ -261,10 +261,8 @@ calltrap:
 	movl	%ebx,%edx
 	xorq	%rax,%rax
 	call	_C_LABEL(printf)
-#ifdef DDB
-	int	$3
-#endif /* DDB */
-	movl	%ebx,CPUVAR(ILEVEL)
+	movl	%ebx,%edi
+	call	_C_LABEL(spllower)
 	jmp	.Lalltraps_checkast
 4:	.asciz	"WARNING: SPL NOT LOWERED ON TRAP EXIT %x %x\n"
 #endif /* DIAGNOSTIC */
diff --git a/sys/arch/i386/i386/trap.c b/sys/arch/i386/i386/trap.c
index 44c932b27334..431fc5b65450 100644
--- a/sys/arch/i386/i386/trap.c
+++ b/sys/arch/i386/i386/trap.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: trap.c,v 1.227 2007/12/02 16:37:58 ad Exp $	*/
+/*	$NetBSD: trap.c,v 1.228 2007/12/03 20:21:33 ad Exp $	*/
 
 /*-
  * Copyright (c) 1998, 2000, 2005 The NetBSD Foundation, Inc.
@@ -75,7 +75,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: trap.c,v 1.227 2007/12/02 16:37:58 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: trap.c,v 1.228 2007/12/03 20:21:33 ad Exp $");
 
 #include "opt_ddb.h"
 #include "opt_kgdb.h"
@@ -530,9 +530,7 @@ copyfault:
 		uvmexp.softs++;
 		if (l->l_pflag & LP_OWEUPC) {
 			l->l_pflag &= ~LP_OWEUPC;
-			KERNEL_LOCK(1, l);
 			ADDUPROF(l);
-			KERNEL_UNLOCK_LAST(l);
 		}
 		/* Allow a forced task switch. */
 		if (curcpu()->ci_want_resched)
diff --git a/sys/arch/i386/i386/vector.S b/sys/arch/i386/i386/vector.S
index f3a9de4c7578..216b8704633c 100644
--- a/sys/arch/i386/i386/vector.S
+++ b/sys/arch/i386/i386/vector.S
@@ -1,4 +1,4 @@
-/*	$NetBSD: vector.S,v 1.31 2007/12/03 15:33:46 ad Exp $	*/
+/*	$NetBSD: vector.S,v 1.32 2007/12/03 20:21:33 ad Exp $	*/
 
 /*
  * Copyright 2002 (c) Wasabi Systems, Inc.
@@ -901,10 +901,9 @@ calltrap:
 	pushl	$4f
 	call	_C_LABEL(printf)
 	addl	$4,%esp
-#ifdef DDB
-	int	$3
-#endif /* DDB */
-	movl	%ebx,CPUVAR(ILEVEL)
+	pushl	%ebx
+	call	_C_LABEL(spllower)
+	addl	$4,%esp
 	jmp	.Lalltraps_checkast	/* re-check ASTs */
 4:	.asciz	"WARNING: SPL NOT LOWERED ON TRAP EXIT\n"
 #endif /* DIAGNOSTIC */