From: Martin Pieuchot <mpi@grenadille.net>
Subject: cpu_exit() diet
To: tech@openbsd.org
Date: Fri, 16 May 2025 16:31:23 +0200

Diff below moves pmap_deactivate() and sched_exit() outside of
cpu_exit(). 

The order of operations change for i386 and mips64:

 - For i386 pmap_deactivate() was missing but since it's a no-op it's fine.

 - For mips64 pmap_deactivate() was called before restoring `p_addr'.  It's
   also harmless because it only clears the curpmap pointer.

I tested this on arm64, amd64 and i386.  I'd appreciate tests on other
architectures to ensure there's no mistake.

ok?

Index: kern/kern_exit.c
===================================================================
RCS file: /cvs/src/sys/kern/kern_exit.c,v
diff -u -p -r1.246 kern_exit.c
--- kern/kern_exit.c	16 May 2025 13:40:30 -0000	1.246
+++ kern/kern_exit.c	16 May 2025 14:13:41 -0000
@@ -382,16 +382,21 @@ exit1(struct proc *p, int xexit, int xsi
 	 */
 
 	/*
-	 * Finally, call machine-dependent code to switch to a new
-	 * context (possibly the idle context).  Once we are no longer
-	 * using the dead process's vmspace and stack, exit2() will be
-	 * called to schedule those resources to be released by the
-	 * reaper thread.
-	 *
-	 * Note that cpu_exit() will end with a call equivalent to
-	 * cpu_switch(), finishing our execution (pun intended).
+	 * Finally, call machine-dependent code.
 	 */
 	cpu_exit(p);
+
+	/*
+	 * Deactivate the exiting address space before the vmspace
+	 * is freed.  Note that we will continue to run on this
+	 * vmspace's context until the switch to idle in sched_exit().
+	 *
+	 * Once we are no longer using the dead process's vmspace and
+	 * stack, exit2() will be called to schedule those resources
+	 * to be released by the reaper thread.
+	 */
+	pmap_deactivate(p);
+	sched_exit(p);
 	panic("cpu_exit returned");
 }
 
Index: arch/alpha/alpha/locore.s
===================================================================
RCS file: /cvs/src/sys/arch/alpha/alpha/locore.s,v
diff -u -p -r1.57 locore.s
--- arch/alpha/alpha/locore.s	28 Apr 2025 13:27:20 -0000	1.57
+++ arch/alpha/alpha/locore.s	16 May 2025 14:13:41 -0000
@@ -653,7 +653,7 @@ LEAF(cpu_switchto, 2)
 	 * We don't deactivate if we came here from sched_exit
 	 * (old pmap no longer exists; vmspace has been freed).
 	 * oldproc will be NULL in this case.  We have actually
-	 * taken care of calling pmap_deactivate() in cpu_exit(),
+	 * taken care of calling pmap_deactivate() in exit1(),
 	 * before the vmspace went away.
 	 */
 	beq	s0, 2f
Index: arch/alpha/alpha/vm_machdep.c
===================================================================
RCS file: /cvs/src/sys/arch/alpha/alpha/vm_machdep.c,v
diff -u -p -r1.53 vm_machdep.c
--- arch/alpha/alpha/vm_machdep.c	21 May 2024 23:16:06 -0000	1.53
+++ arch/alpha/alpha/vm_machdep.c	16 May 2025 14:13:41 -0000
@@ -45,25 +45,11 @@
 #include <machine/reg.h>
 
 
-/*
- * cpu_exit is called as the last action during exit.
- */
 void
-cpu_exit(p)
-	struct proc *p;
+cpu_exit(struct proc *p)
 {
-
 	if (p->p_addr->u_pcb.pcb_fpcpu != NULL)
 		fpusave_proc(p, 0);
-
-	/*
-	 * Deactivate the exiting address space before the vmspace
-	 * is freed.  Note that we will continue to run on this
-	 * vmspace's context until the switch to idle in sched_exit().
-	 */
-	pmap_deactivate(p);
-	sched_exit(p);
-	/* NOTREACHED */
 }
 
 /*
Index: arch/amd64/amd64/vm_machdep.c
===================================================================
RCS file: /cvs/src/sys/arch/amd64/amd64/vm_machdep.c,v
diff -u -p -r1.49 vm_machdep.c
--- arch/amd64/amd64/vm_machdep.c	24 Oct 2024 17:37:03 -0000	1.49
+++ arch/amd64/amd64/vm_machdep.c	16 May 2025 14:13:41 -0000
@@ -116,17 +116,9 @@ cpu_fork(struct proc *p1, struct proc *p
 	pcb->pcb_rbp = 0;
 }
 
-/*
- * cpu_exit is called as the last action during exit.
- *
- * We clean up a little and then call sched_exit() with the old proc as an
- * argument.
- */
 void
 cpu_exit(struct proc *p)
 {
-	pmap_deactivate(p);
-	sched_exit(p);
 }
 
 /*
Index: arch/arm/arm/vm_machdep.c
===================================================================
RCS file: /cvs/src/sys/arch/arm/arm/vm_machdep.c,v
diff -u -p -r1.29 vm_machdep.c
--- arch/arm/arm/vm_machdep.c	11 Apr 2023 00:45:07 -0000	1.29
+++ arch/arm/arm/vm_machdep.c	16 May 2025 14:13:41 -0000
@@ -130,9 +130,6 @@ cpu_exit(struct proc *p)
 	/* If we were using the FPU, forget about it. */
 	if (p->p_addr->u_pcb.pcb_fpcpu != NULL)
 		vfp_discard(p);
-
-	pmap_deactivate(p);
-	sched_exit(p);
 }
 
 struct kmem_va_mode kv_physwait = {
Index: arch/arm64/arm64/vm_machdep.c
===================================================================
RCS file: /cvs/src/sys/arch/arm64/arm64/vm_machdep.c,v
diff -u -p -r1.13 vm_machdep.c
--- arch/arm64/arm64/vm_machdep.c	31 Jan 2025 20:49:25 -0000	1.13
+++ arch/arm64/arm64/vm_machdep.c	16 May 2025 14:13:41 -0000
@@ -112,17 +112,9 @@ cpu_fork(struct proc *p1, struct proc *p
 	pcb->pcb_sp = (uint64_t)sf;
 }
 
-/*
- * cpu_exit is called as the last action during exit.
- *
- * We clean up a little and then call sched_exit() with the old proc as an
- * argument.
- */
 void
 cpu_exit(struct proc *p)
 {
-	pmap_deactivate(p);
-	sched_exit(p);
 }
 
 struct kmem_va_mode kv_physwait = {
Index: arch/hppa/hppa/vm_machdep.c
===================================================================
RCS file: /cvs/src/sys/arch/hppa/hppa/vm_machdep.c,v
diff -u -p -r1.85 vm_machdep.c
--- arch/hppa/hppa/vm_machdep.c	25 Oct 2022 15:15:38 -0000	1.85
+++ arch/hppa/hppa/vm_machdep.c	16 May 2025 14:13:41 -0000
@@ -131,9 +131,6 @@ cpu_exit(struct proc *p)
 	fpu_proc_flush(p);
 
 	pool_put(&hppa_fppl, pcb->pcb_fpstate);
-
-	pmap_deactivate(p);
-	sched_exit(p);
 }
 
 struct kmem_va_mode kv_physwait = {
Index: arch/i386/i386/vm_machdep.c
===================================================================
RCS file: /cvs/src/sys/arch/i386/i386/vm_machdep.c,v
diff -u -p -r1.74 vm_machdep.c
--- arch/i386/i386/vm_machdep.c	11 Apr 2023 00:45:07 -0000	1.74
+++ arch/i386/i386/vm_machdep.c	16 May 2025 14:13:41 -0000
@@ -103,9 +103,6 @@ cpu_fork(struct proc *p1, struct proc *p
 	pcb->pcb_ebp = 0;
 }
 
-/*
- * cpu_exit is called as the last action during exit.
- */
 void
 cpu_exit(struct proc *p)
 {
@@ -114,7 +111,6 @@ cpu_exit(struct proc *p)
 	if (p->p_addr->u_pcb.pcb_fpcpu != NULL)
 		npxsave_proc(p, 0);
 #endif
-	sched_exit(p);
 }
 
 /*
Index: arch/m88k/m88k/vm_machdep.c
===================================================================
RCS file: /cvs/src/sys/arch/m88k/m88k/vm_machdep.c,v
diff -u -p -r1.30 vm_machdep.c
--- arch/m88k/m88k/vm_machdep.c	5 Jun 2024 19:22:04 -0000	1.30
+++ arch/m88k/m88k/vm_machdep.c	16 May 2025 14:13:41 -0000
@@ -108,14 +108,9 @@ cpu_fork(struct proc *p1, struct proc *p
 	mdpcb->pcb_pc = (u_int)proc_trampoline;
 }
 
-/*
- * cpu_exit is called as the last action during exit.
- */
 void
 cpu_exit(struct proc *p)
 {
-	pmap_deactivate(p);
-	sched_exit(p);
 }
 
 struct kmem_va_mode kv_physwait = {
Index: arch/mips64/mips64/vm_machdep.c
===================================================================
RCS file: /cvs/src/sys/arch/mips64/mips64/vm_machdep.c,v
diff -u -p -r1.42 vm_machdep.c
--- arch/mips64/mips64/vm_machdep.c	22 May 2022 16:54:17 -0000	1.42
+++ arch/mips64/mips64/vm_machdep.c	16 May 2025 14:13:41 -0000
@@ -125,9 +125,6 @@ cpu_fork(struct proc *p1, struct proc *p
 	pcb->pcb_context.val[0] = (register_t)func;
 }
 
-/*
- * cpu_exit is called as the last action during exit.
- */
 void
 cpu_exit(struct proc *p)
 {
@@ -136,12 +133,10 @@ cpu_exit(struct proc *p)
 	if (ci->ci_fpuproc == p)
 		ci->ci_fpuproc = NULL;
 
-	pmap_deactivate(p);
 #if UPAGES == 1
 	/* restore p_addr for proper deallocation */
 	p->p_addr = (void *)p->p_md.md_uarea;
 #endif
-	sched_exit(p);
 }
 
 struct kmem_va_mode kv_physwait = {
Index: arch/powerpc/powerpc/vm_machdep.c
===================================================================
RCS file: /cvs/src/sys/arch/powerpc/powerpc/vm_machdep.c,v
diff -u -p -r1.55 vm_machdep.c
--- arch/powerpc/powerpc/vm_machdep.c	11 Apr 2023 00:45:07 -0000	1.55
+++ arch/powerpc/powerpc/vm_machdep.c	16 May 2025 14:13:41 -0000
@@ -130,10 +130,6 @@ cpu_fork(struct proc *p1, struct proc *p
 }
 
 /*
- * cpu_exit is called as the last action during exit.
- * We release the address space and machine-dependent resources,
- * including the memory for the user structure and kernel stack.
- *
  * Since we don't have curproc anymore, we cannot sleep, and therefore
  * this is at least incorrect for the multiprocessor version.
  * Not sure whether we can get away with this in the single proc version.		XXX
@@ -157,9 +153,6 @@ cpu_exit(struct proc *p)
 	if (pcb->pcb_vr != NULL)
 		pool_put(&ppc_vecpl, pcb->pcb_vr);
 #endif /* ALTIVEC */
-	
-	pmap_deactivate(p);
-	sched_exit(p);
 }
 
 struct kmem_va_mode kv_physwait = {
Index: arch/powerpc64/powerpc64/vm_machdep.c
===================================================================
RCS file: /cvs/src/sys/arch/powerpc64/powerpc64/vm_machdep.c,v
diff -u -p -r1.9 vm_machdep.c
--- arch/powerpc64/powerpc64/vm_machdep.c	11 Apr 2023 00:45:08 -0000	1.9
+++ arch/powerpc64/powerpc64/vm_machdep.c	16 May 2025 14:13:41 -0000
@@ -113,17 +113,9 @@ cpu_fork(struct proc *p1, struct proc *p
 	pcb->pcb_sp = (register_t)sf;
 }
 
-/*
- * cpu_exit is called as the last action during exit.
- *
- * We clean up a little and then call sched_exit() with the old proc as an
- * argument.
- */
 void
 cpu_exit(struct proc *p)
 {
-	pmap_deactivate(p);
-	sched_exit(p);
 }
 
 struct kmem_va_mode kv_physwait = {
Index: arch/riscv64/riscv64/vm_machdep.c
===================================================================
RCS file: /cvs/src/sys/arch/riscv64/riscv64/vm_machdep.c,v
diff -u -p -r1.11 vm_machdep.c
--- arch/riscv64/riscv64/vm_machdep.c	11 Apr 2023 00:45:08 -0000	1.11
+++ arch/riscv64/riscv64/vm_machdep.c	16 May 2025 14:13:41 -0000
@@ -104,17 +104,9 @@ cpu_fork(struct proc *p1, struct proc *p
 	pcb->pcb_sp = (uint64_t)sf;
 }
 
-/*
- * cpu_exit is called as the last action during exit.
- *
- * We clean up a little and then call sched_exit() with the old proc as an
- * argument.
- */
 void
 cpu_exit(struct proc *p)
 {
-	pmap_deactivate(p);
-	sched_exit(p);
 }
 
 struct kmem_va_mode kv_physwait = {
Index: arch/sh/sh/locore_c.c
===================================================================
RCS file: /cvs/src/sys/arch/sh/sh/locore_c.c,v
diff -u -p -r1.14 locore_c.c
--- arch/sh/sh/locore_c.c	6 Jan 2023 19:10:18 -0000	1.14
+++ arch/sh/sh/locore_c.c	16 May 2025 14:13:41 -0000
@@ -156,9 +156,6 @@ cpu_exit(struct proc *p)
 {
 	if (p->p_md.md_flags & MDP_STEP)
 		_reg_write_2(SH_(BBRB), 0);
-
-	pmap_deactivate(p);
-	sched_exit(p);
 }
 
 #ifndef P1_STACK
Index: arch/sparc64/sparc64/vm_machdep.c
===================================================================
RCS file: /cvs/src/sys/arch/sparc64/sparc64/vm_machdep.c,v
diff -u -p -r1.45 vm_machdep.c
--- arch/sparc64/sparc64/vm_machdep.c	29 Mar 2024 21:27:53 -0000	1.45
+++ arch/sparc64/sparc64/vm_machdep.c	16 May 2025 14:13:41 -0000
@@ -269,13 +269,6 @@ fpusave_proc(struct proc *p, int save)
 #endif
 }
 
-/*
- * cpu_exit is called as the last action during exit.
- *
- * We clean up a little and then call sched_exit() with the old proc
- * as an argument.  sched_exit() schedules the old vmspace and stack
- * to be freed, then selects a new process to run.
- */
 void
 cpu_exit(struct proc *p)
 {
@@ -284,9 +277,6 @@ cpu_exit(struct proc *p)
 		free(p->p_md.md_fpstate, M_SUBPROC, sizeof(struct fpstate));
 		p->p_md.md_fpstate = NULL;
 	}
-
-	pmap_deactivate(p);
-	sched_exit(p);
 }