Re: SMP busted on non-cpu-hotplug systems

["David S. Miller" <davem@davemloft.net>]

From: Andrew Morton <akpm@osdl.org>
Date: Sat, 25 Mar 2006 03:47:44 -0800

> I think it'd be cleanest to require that the arch do that -
> fixup_cpu_present_map() looks like a bit of a hack.

Indeed it does.  I'm planning on doing someting like this
for sparc64:

diff --git a/arch/sparc64/kernel/smp.c b/arch/sparc64/kernel/smp.c
index 1b6e2ad..7dc28a4 100644
--- a/arch/sparc64/kernel/smp.c
+++ b/arch/sparc64/kernel/smp.c
@@ -1298,6 +1298,7 @@ void __init smp_prepare_cpus(unsigned in
 		while (!cpu_find_by_instance(instance, NULL, &mid)) {
 			if (mid != boot_cpu_id) {
 				cpu_clear(mid, phys_cpu_present_map);
+				cpu_clear(mid, cpu_present_map);
 				if (num_possible_cpus() <= max_cpus)
 					break;
 			}
@@ -1332,8 +1333,10 @@ void __init smp_setup_cpu_possible_map(v
 
 	instance = 0;
 	while (!cpu_find_by_instance(instance, NULL, &mid)) {
-		if (mid < NR_CPUS)
+		if (mid < NR_CPUS) {
 			cpu_set(mid, phys_cpu_present_map);
+			cpu_set(mid, cpu_present_map);
+		}
 		instance++;
 	}
 }