Add code to stop scheduling processes on CPUs, effectively halting that CPU.

Use this to do a shutdown with only the boot processor running.  This should
avoid nasty races during shutdown.

help from art@, ok deraadt@, miod@

3 files changed, 42 insertions, 4 deletions

diff --git a/sys/kern/kern_sched.c b/sys/kern/kern_sched.c
index 58b2ab73436..7625440b7ee 100644
--- a/sys/kern/kern_sched.c
+++ b/sys/kern/kern_sched.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_sched.c,v 1.16 2009/11/29 23:12:30 kettenis Exp $	*/
+/*	$OpenBSD: kern_sched.c,v 1.17 2010/01/09 02:44:17 kettenis Exp $	*/
 /*
  * Copyright (c) 2007, 2008 Artur Grabowski <art@openbsd.org>
  *
@@ -148,8 +148,14 @@ sched_idle(void *v)
 
 		cpuset_add(&sched_idle_cpus, ci);
 		cpu_idle_enter();
-		while (spc->spc_whichqs == 0)
+		while (spc->spc_whichqs == 0) {
+			if (spc->spc_schedflags & SPCF_SHOULDHALT) {
+				atomic_setbits_int(&spc->spc_schedflags,
+				    SPCF_HALTED);
+				wakeup(spc);
+			}
 			cpu_idle_cycle();
+		}
 		cpu_idle_leave();
 		cpuset_del(&sched_idle_cpus, ci);
 	}
@@ -246,6 +252,13 @@ sched_chooseproc(void)
 
 	SCHED_ASSERT_LOCKED();
 
+	if (spc->spc_schedflags & SPCF_SHOULDHALT) {
+		p = spc->spc_idleproc;
+		KASSERT(p);
+		p->p_stat = SRUN;
+		return (p);
+	}
+
 again:
 	if (spc->spc_whichqs) {
 		queue = ffs(spc->spc_whichqs) - 1;
diff --git a/sys/kern/kern_xxx.c b/sys/kern/kern_xxx.c
index 654ed83dc4f..359c97541f2 100644
--- a/sys/kern/kern_xxx.c
+++ b/sys/kern/kern_xxx.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_xxx.c,v 1.14 2009/11/29 23:12:30 kettenis Exp $	*/
+/*	$OpenBSD: kern_xxx.c,v 1.15 2010/01/09 02:44:17 kettenis Exp $	*/
 /*	$NetBSD: kern_xxx.c,v 1.32 1996/04/22 01:38:41 christos Exp $	*/
 
 /*
@@ -68,6 +68,29 @@ sys_reboot(struct proc *p, void *v, register_t *retval)
 		}
 	}
 
+	/*
+	 * Make sure we stop the secondary CPUs.
+	 */
+	CPU_INFO_FOREACH(cii, ci) {
+		struct schedstate_percpu *spc = &ci->ci_schedstate;
+
+		if (CPU_IS_PRIMARY(ci))
+			continue;
+		atomic_setbits_int(&spc->spc_schedflags, SPCF_SHOULDHALT);
+	}
+	CPU_INFO_FOREACH(cii, ci) {
+		struct schedstate_percpu *spc = &ci->ci_schedstate;
+		struct sleep_state sls;
+
+		if (CPU_IS_PRIMARY(ci))
+			continue;
+		while ((spc->spc_schedflags & SPCF_HALTED) == 0) {
+			sleep_setup(&sls, spc, PZERO, "schedstate");
+			sleep_finish(&sls,
+			    (spc->spc_schedflags & SPCF_HALTED) == 0);
+		}
+	}
+
 	if_downall();
 
 	boot(SCARG(uap, opt));
diff --git a/sys/sys/sched.h b/sys/sys/sched.h
index 5e5d9297bbd..9304a631628 100644
--- a/sys/sys/sched.h
+++ b/sys/sys/sched.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: sched.h,v 1.24 2009/11/29 23:12:30 kettenis Exp $	*/
+/*	$OpenBSD: sched.h,v 1.25 2010/01/09 02:44:17 kettenis Exp $	*/
 /* $NetBSD: sched.h,v 1.2 1999/02/28 18:14:58 ross Exp $ */
 
 /*-
@@ -122,6 +122,8 @@ struct schedstate_percpu {
 #define SPCF_SEENRR             0x0001  /* process has seen roundrobin() */
 #define SPCF_SHOULDYIELD        0x0002  /* process should yield the CPU */
 #define SPCF_SWITCHCLEAR        (SPCF_SEENRR|SPCF_SHOULDYIELD)
+#define SPCF_SHOULDHALT		0x0004	/* CPU should be vacated */
+#define SPCF_HALTED		0x0008	/* CPU has been halted */
 
 #define	SCHED_PPQ	(128 / SCHED_NQS)	/* priorities per queue */
 #define NICE_WEIGHT 2			/* priorities per nice level */