[sched] fix sched_domains hotplug bootstrap ordering vs. cpu_online_map issue

[William Lee Irwin III <wli@holomorphy.com>]

William Lee Irwin III <wli@holomorphy.com> wrote:
>> This is the whole thing; the "other half" referred to a new hunk added to
>> the patch (identical to this one) posted in its entirety.

On Fri, Sep 03, 2004 at 03:34:34PM -0700, Andrew Morton wrote:
> ho-hum. changelog, please?

cpu_online_map is not set up at the time of sched domain initialization
when hotplug cpu paths are used for SMP booting. At this phase of
bootstrapping, cpu_possible_map can be used by the various
architectures using cpu hotplugging for SMP bootstrap, but the
manipulations of cpu_online_map done on behalf of NUMA architectures,
done indirectly via node_to_cpumask(), can't, because cpu_online_map
starts depopulated and hasn't yet been populated. On true NUMA
architectures this is a distinct cpumask_t from cpu_online_map and so
the unpatched code works on NUMA; on non-NUMA architectures the
definition of node_to_cpumask() this way breaks and would require an
invasive sweeping of users of node_to_cpumask() to change it to e.g.
cpu_possible_map, as cpu_possible_map is not suitable for use at
runtime as a substitute for cpu_online_map.

Signed-off-by: William Irwin <wli@holomorphy.com>


Index: wait-2.6.9-rc1-mm1/kernel/sched.c
===================================================================
--- wait-2.6.9-rc1-mm1.orig/kernel/sched.c	2004-08-28 11:41:47.000000000 -0700
+++ wait-2.6.9-rc1-mm1/kernel/sched.c	2004-08-29 10:46:52.543081208 -0700
@@ -4224,7 +4224,11 @@
 		sd = &per_cpu(phys_domains, i);
 		group = cpu_to_phys_group(i);
 		*sd = SD_CPU_INIT;
+#ifdef CONFIG_NUMA
 		sd->span = nodemask;
+#else
+		sd->span = cpu_possible_map;
+#endif
 		sd->parent = p;
 		sd->groups = &sched_group_phys[group];
 
@@ -4262,6 +4266,7 @@
 						&cpu_to_isolated_group);
 	}
 
+#ifdef CONFIG_NUMA
 	/* Set up physical groups */
 	for (i = 0; i < MAX_NUMNODES; i++) {
 		cpumask_t nodemask = node_to_cpumask(i);
@@ -4273,6 +4278,10 @@
 		init_sched_build_groups(sched_group_phys, nodemask,
 						&cpu_to_phys_group);
 	}
+#else
+	init_sched_build_groups(sched_group_phys, cpu_possible_map,
+							&cpu_to_phys_group);
+#endif
 
 #ifdef CONFIG_NUMA
 	/* Set up node groups */