oprofile/x86: protect cpu hotplug sections

This patch reworks oprofile cpu hotplug code as follows:

Introduce ctr_running variable to check, if counters are running or
not. The state must be known for taking a cpu on or offline and when
switching counters during counter multiplexing.

Protect on_each_cpu() sections with get_online_cpus()/put_online_cpu()
functions. This is necessary if notifiers or states are
modified. Within these sections the cpu mask may not change.

Switch only between counters in nmi_cpu_switch(), if counters are
running. Otherwise the switch may restart a counter though they are
disabled.

Add nmi_cpu_setup() and nmi_cpu_shutdown() to cpu hotplug code. The
function must also be called to avoid uninitialzed counter usage.

Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Robert Richter <robert.richter@amd.com>

arch/x86/oprofile/nmi_int.c

@@ -31,8 +31,9 @@ static struct op_x86_model_spec *model;
 static DEFINE_PER_CPU(struct op_msrs, cpu_msrs);
 static DEFINE_PER_CPU(unsigned long, saved_lvtpc);
 
-/* 0 == registered but off, 1 == registered and on */
-static int nmi_enabled = 0;
+/* must be protected with get_online_cpus()/put_online_cpus(): */
+static int nmi_enabled;
+static int ctr_running;
 
 struct op_counter_config counter_config[OP_MAX_COUNTER];
 
@@ -103,7 +104,10 @@ static void nmi_cpu_start(void *dummy)
 
 static int nmi_start(void)
 {
+	get_online_cpus();
 	on_each_cpu(nmi_cpu_start, NULL, 1);
+	ctr_running = 1;
+	put_online_cpus();
 	return 0;
 }
 
@@ -118,7 +122,10 @@ static void nmi_cpu_stop(void *dummy)
 
 static void nmi_stop(void)
 {
+	get_online_cpus();
 	on_each_cpu(nmi_cpu_stop, NULL, 1);
+	ctr_running = 0;
+	put_online_cpus();
 }
 
 #ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX
@@ -258,7 +265,10 @@ static int nmi_switch_event(void)
 	if (nmi_multiplex_on() < 0)
 		return -EINVAL;		/* not necessary */
 
-	on_each_cpu(nmi_cpu_switch, NULL, 1);
+	get_online_cpus();
+	if (ctr_running)
+		on_each_cpu(nmi_cpu_switch, NULL, 1);
+	put_online_cpus();
 
 	return 0;
 }
@@ -386,8 +396,11 @@ static int nmi_setup(void)
 	if (err)
 		goto fail;
 
+	get_online_cpus();
 	on_each_cpu(nmi_cpu_setup, NULL, 1);
 	nmi_enabled = 1;
+	put_online_cpus();
+
 	return 0;
 fail:
 	free_msrs();
@@ -433,8 +446,11 @@ static void nmi_shutdown(void)
 {
 	struct op_msrs *msrs;
 
-	nmi_enabled = 0;
+	get_online_cpus();
 	on_each_cpu(nmi_cpu_shutdown, NULL, 1);
+	nmi_enabled = 0;
+	ctr_running = 0;
+	put_online_cpus();
 	unregister_die_notifier(&profile_exceptions_nb);
 	msrs = &get_cpu_var(cpu_msrs);
 	model->shutdown(msrs);
@@ -442,6 +458,22 @@ static void nmi_shutdown(void)
 	put_cpu_var(cpu_msrs);
 }
 
+static void nmi_cpu_up(void *dummy)
+{
+	if (nmi_enabled)
+		nmi_cpu_setup(dummy);
+	if (ctr_running)
+		nmi_cpu_start(dummy);
+}
+
+static void nmi_cpu_down(void *dummy)
+{
+	if (ctr_running)
+		nmi_cpu_stop(dummy);
+	if (nmi_enabled)
+		nmi_cpu_shutdown(dummy);
+}
+
 static int nmi_create_files(struct super_block *sb, struct dentry *root)
 {
 	unsigned int i;
@@ -478,10 +510,10 @@ static int oprofile_cpu_notifier(struct notifier_block *b, unsigned long action,
 	switch (action) {
 	case CPU_DOWN_FAILED:
 	case CPU_ONLINE:
-		smp_call_function_single(cpu, nmi_cpu_start, NULL, 0);
+		smp_call_function_single(cpu, nmi_cpu_up, NULL, 0);
 		break;
 	case CPU_DOWN_PREPARE:
-		smp_call_function_single(cpu, nmi_cpu_stop, NULL, 1);
+		smp_call_function_single(cpu, nmi_cpu_down, NULL, 1);
 		break;
 	}
 	return NOTIFY_DONE;
@@ -699,7 +731,11 @@ int __init op_nmi_init(struct oprofile_operations *ops)
 		return -ENODEV;
 	}
 
+	get_online_cpus();
 	register_cpu_notifier(&oprofile_cpu_nb);
+	nmi_enabled = 0;
+	ctr_running = 0;
+	put_online_cpus();
 
 	/* default values, can be overwritten by model */
 	ops->create_files	= nmi_create_files;
@@ -729,7 +765,11 @@ void op_nmi_exit(void)
 {
 	if (using_nmi) {
 		exit_sysfs();
+		get_online_cpus();
 		unregister_cpu_notifier(&oprofile_cpu_nb);
+		nmi_enabled = 0;
+		ctr_running = 0;
+		put_online_cpus();
 	}
 	if (model->exit)
 		model->exit();