sched: add arch_update_cpu_topology hook.

Will be called each time the scheduling domains are rebuild.
Needed for architectures that don't have a static cpu topology.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/topology.h b/include/linux/topology.h
index 2d8dac8..bd14f8b 100644
--- a/include/linux/topology.h
+++ b/include/linux/topology.h
@@ -50,6 +50,8 @@
 	for_each_online_node(node)						\
 		if (nr_cpus_node(node))
 
+void arch_update_cpu_topology(void);
+
 /* Conform to ACPI 2.0 SLIT distance definitions */
 #define LOCAL_DISTANCE		10
 #define REMOTE_DISTANCE		20
diff --git a/kernel/sched.c b/kernel/sched.c
index 78482e5..28c73f0 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6807,6 +6807,10 @@
  */
 static cpumask_t fallback_doms;
 
+void __attribute__((weak)) arch_update_cpu_topology(void)
+{
+}
+
 /*
  * Set up scheduler domains and groups. Callers must hold the hotplug lock.
  * For now this just excludes isolated cpus, but could be used to
@@ -6816,6 +6820,7 @@
 {
 	int err;
 
+	arch_update_cpu_topology();
 	ndoms_cur = 1;
 	doms_cur = kmalloc(sizeof(cpumask_t), GFP_KERNEL);
 	if (!doms_cur)