x86: cpumask: x86 mmio-mod.c use cpumask_var_t for downed_cpus

Impact: cleanup, reduce memory usage for CONFIG_CPUMASK_OFFSTACK=y

Part of the "getting rid of obsolete cpumask_t" patch:

 1) Use cpumask_var_t: this is a pointer if CONFIG_CPUMASK_OFFSTACK=y
 2) Call alloc_cpumask_var() on first entry into enter_uniprocessor()
 3) Use modern cpumask_* functions.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Pekka Paalanen <pq@iki.fi>
LKML-Reference: <200903111633.55952.rusty@rustcorp.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/mm/mmio-mod.c

@@ -378,27 +378,34 @@ static void clear_trace_list(void)
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
-static cpumask_t downed_cpus;
+static cpumask_var_t downed_cpus;
 
 static void enter_uniprocessor(void)
 {
 	int cpu;
 	int err;
 
+	if (downed_cpus == NULL &&
+	    !alloc_cpumask_var(&downed_cpus, GFP_KERNEL)) {
+		pr_notice(NAME "Failed to allocate mask\n");
+		goto out;
+	}
+
 	get_online_cpus();
-	downed_cpus = cpu_online_map;
-	cpu_clear(first_cpu(cpu_online_map), downed_cpus);
+	cpumask_copy(downed_cpus, cpu_online_mask);
+	cpumask_clear_cpu(cpumask_first(cpu_online_mask), downed_cpus);
 	if (num_online_cpus() > 1)
 		pr_notice(NAME "Disabling non-boot CPUs...\n");
 	put_online_cpus();
 
-	for_each_cpu_mask(cpu, downed_cpus) {
+	for_each_cpu(cpu, downed_cpus) {
 		err = cpu_down(cpu);
 		if (!err)
 			pr_info(NAME "CPU%d is down.\n", cpu);
 		else
 			pr_err(NAME "Error taking CPU%d down: %d\n", cpu, err);
 	}
+out:
 	if (num_online_cpus() > 1)
 		pr_warning(NAME "multiple CPUs still online, "
 						"may miss events.\n");
@@ -411,10 +418,10 @@ static void __ref leave_uniprocessor(void)
 	int cpu;
 	int err;
 
-	if (cpus_weight(downed_cpus) == 0)
+	if (downed_cpus == NULL || cpumask_weight(downed_cpus) == 0)
 		return;
 	pr_notice(NAME "Re-enabling CPUs...\n");
-	for_each_cpu_mask(cpu, downed_cpus) {
+	for_each_cpu(cpu, downed_cpus) {
 		err = cpu_up(cpu);
 		if (!err)
 			pr_info(NAME "enabled CPU%d.\n", cpu);