sched: domain sysctl fixes: unregister the sysctl table before domains

Unregister and free the sysctl table before destroying domains, then
rebuild and register after creating the new domains.  This prevents the
sysctl table from pointing to freed memory for root to write.
Signed-off-by: Milton Miller <miltonm@bga.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/sched.c

@@ -5250,6 +5250,18 @@ static struct ctl_table *sd_alloc_ctl_entry(int n)
 	return entry;
 }
 
+static void sd_free_ctl_entry(struct ctl_table **tablep)
+{
+	struct ctl_table *entry = *tablep;
+
+	for (entry = *tablep; entry->procname; entry++)
+		if (entry->child)
+			sd_free_ctl_entry(&entry->child);
+
+	kfree(*tablep);
+	*tablep = NULL;
+}
+
 static void
 set_table_entry(struct ctl_table *entry,
 		const char *procname, void *data, int maxlen,
@@ -5318,7 +5330,7 @@ static ctl_table *sd_alloc_ctl_cpu_table(int cpu)
 }
 
 static struct ctl_table_header *sd_sysctl_header;
-static void init_sched_domain_sysctl(void)
+static void register_sched_domain_sysctl(void)
 {
 	int i, cpu_num = num_online_cpus();
 	struct ctl_table *entry = sd_alloc_ctl_entry(cpu_num + 1);
@@ -5335,8 +5347,18 @@ static void init_sched_domain_sysctl(void)
 	}
 	sd_sysctl_header = register_sysctl_table(sd_ctl_root);
 }
+
+static void unregister_sched_domain_sysctl(void)
+{
+	unregister_sysctl_table(sd_sysctl_header);
+	sd_sysctl_header = NULL;
+	sd_free_ctl_entry(&sd_ctl_dir[0].child);
+}
 #else
-static void init_sched_domain_sysctl(void)
+static void register_sched_domain_sysctl(void)
+{
+}
+static void unregister_sched_domain_sysctl(void)
 {
 }
 #endif
@@ -6271,6 +6293,8 @@ static int arch_init_sched_domains(const cpumask_t *cpu_map)
 
 	err = build_sched_domains(&cpu_default_map);
 
+	register_sched_domain_sysctl();
+
 	return err;
 }
 
@@ -6287,6 +6311,8 @@ static void detach_destroy_domains(const cpumask_t *cpu_map)
 {
 	int i;
 
+	unregister_sched_domain_sysctl();
+
 	for_each_cpu_mask(i, *cpu_map)
 		cpu_attach_domain(NULL, i);
 	synchronize_sched();
@@ -6317,6 +6343,8 @@ int partition_sched_domains(cpumask_t *partition1, cpumask_t *partition2)
 	if (!err && !cpus_empty(*partition2))
 		err = build_sched_domains(partition2);
 
+	register_sched_domain_sysctl();
+
 	return err;
 }
 
@@ -6448,8 +6476,6 @@ void __init sched_init_smp(void)
 	/* XXX: Theoretical race here - CPU may be hotplugged now */
 	hotcpu_notifier(update_sched_domains, 0);
 
-	init_sched_domain_sysctl();
-
 	/* Move init over to a non-isolated CPU */
 	if (set_cpus_allowed(current, non_isolated_cpus) < 0)
 		BUG();