[CPUFREQ] cpumask: avoid playing with cpus_allowed in speedstep-ich.c

Impact: don't play with current's cpumask

It's generally a very bad idea to mug some process's cpumask: it could
legitimately and reasonably be changed by root, which could break us
(if done before our code) or them (if we restore the wrong value).

We use smp_call_function_single: this had the advantage of being more
efficient, too.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
To: cpufreq@vger.kernel.org
Cc: Dominik Brodowski <linux@brodo.de>
Signed-off-by: Dave Jones <davej@redhat.com>

arch/x86/kernel/cpu/cpufreq/speedstep-ich.c

@@ -89,7 +89,8 @@ static int speedstep_find_register(void)
  * speedstep_set_state - set the SpeedStep state
  * @state: new processor frequency state (SPEEDSTEP_LOW or SPEEDSTEP_HIGH)
  *
- *   Tries to change the SpeedStep state.
+ *   Tries to change the SpeedStep state.  Can be called from
+ *   smp_call_function_single.
  */
 static void speedstep_set_state(unsigned int state)
 {
@@ -143,6 +144,11 @@ static void speedstep_set_state(unsigned int state)
 	return;
 }
 
+/* Wrapper for smp_call_function_single. */
+static void _speedstep_set_state(void *_state)
+{
+	speedstep_set_state(*(unsigned int *)_state);
+}
 
 /**
  * speedstep_activate - activate SpeedStep control in the chipset
@@ -226,22 +232,28 @@ static unsigned int speedstep_detect_chipset(void)
 	return 0;
 }
 
-static unsigned int _speedstep_get(const struct cpumask *cpus)
-{
+struct get_freq_data {
 	unsigned int speed;
-	cpumask_t cpus_allowed;
-
-	cpus_allowed = current->cpus_allowed;
-	set_cpus_allowed_ptr(current, cpus);
-	speed = speedstep_get_frequency(speedstep_processor);
-	set_cpus_allowed_ptr(current, &cpus_allowed);
-	dprintk("detected %u kHz as current frequency\n", speed);
-	return speed;
+	unsigned int processor;
+};
+
+static void get_freq_data(void *_data)
+{
+	struct get_freq_data *data = _data;
+
+	data->speed = speedstep_get_frequency(data->processor);
 }
 
 static unsigned int speedstep_get(unsigned int cpu)
 {
-	return _speedstep_get(cpumask_of(cpu));
+	struct get_freq_data data = { .processor = cpu };
+
+	/* You're supposed to ensure CPU is online. */
+	if (smp_call_function_single(cpu, get_freq_data, &data, 1) != 0)
+		BUG();
+
+	dprintk("detected %u kHz as current frequency\n", data.speed);
+	return data.speed;
 }
 
 /**
@@ -257,16 +269,16 @@ static int speedstep_target(struct cpufreq_policy *policy,
 			     unsigned int target_freq,
 			     unsigned int relation)
 {
-	unsigned int newstate = 0;
+	unsigned int newstate = 0, policy_cpu;
 	struct cpufreq_freqs freqs;
-	cpumask_t cpus_allowed;
 	int i;
 
 	if (cpufreq_frequency_table_target(policy, &speedstep_freqs[0],
 				target_freq, relation, &newstate))
 		return -EINVAL;
 
-	freqs.old = _speedstep_get(policy->cpus);
+	policy_cpu = cpumask_any_and(policy->cpus, cpu_online_mask);
+	freqs.old = speedstep_get(policy_cpu);
 	freqs.new = speedstep_freqs[newstate].frequency;
 	freqs.cpu = policy->cpu;
 
@@ -276,20 +288,13 @@ static int speedstep_target(struct cpufreq_policy *policy,
 	if (freqs.old == freqs.new)
 		return 0;
 
-	cpus_allowed = current->cpus_allowed;
-
 	for_each_cpu(i, policy->cpus) {
 		freqs.cpu = i;
 		cpufreq_notify_transition(&freqs, CPUFREQ_PRECHANGE);
 	}
 
-	/* switch to physical CPU where state is to be changed */
-	set_cpus_allowed_ptr(current, policy->cpus);
-
-	speedstep_set_state(newstate);
-
-	/* allow to be run on all CPUs */
-	set_cpus_allowed_ptr(current, &cpus_allowed);
+	smp_call_function_single(policy_cpu, _speedstep_set_state, &newstate,
+				 true);
 
 	for_each_cpu(i, policy->cpus) {
 		freqs.cpu = i;
@@ -312,33 +317,43 @@ static int speedstep_verify(struct cpufreq_policy *policy)
 	return cpufreq_frequency_table_verify(policy, &speedstep_freqs[0]);
 }
 
+struct get_freqs {
+	struct cpufreq_policy *policy;
+	int ret;
+};
+
+static void get_freqs_on_cpu(void *_get_freqs)
+{
+	struct get_freqs *get_freqs = _get_freqs;
+
+	get_freqs->ret =
+		speedstep_get_freqs(speedstep_processor,
+			    &speedstep_freqs[SPEEDSTEP_LOW].frequency,
+			    &speedstep_freqs[SPEEDSTEP_HIGH].frequency,
+			    &get_freqs->policy->cpuinfo.transition_latency,
+			    &speedstep_set_state);
+}
 
 static int speedstep_cpu_init(struct cpufreq_policy *policy)
 {
-	int result = 0;
-	unsigned int speed;
-	cpumask_t cpus_allowed;
+	int result;
+	unsigned int policy_cpu, speed;
+	struct get_freqs gf;
 
 	/* only run on CPU to be set, or on its sibling */
 #ifdef CONFIG_SMP
 	cpumask_copy(policy->cpus, cpu_sibling_mask(policy->cpu));
 #endif
-
-	cpus_allowed = current->cpus_allowed;
-	set_cpus_allowed_ptr(current, policy->cpus);
+	policy_cpu = cpumask_any_and(policy->cpus, cpu_online_mask);
 
 	/* detect low and high frequency and transition latency */
-	result = speedstep_get_freqs(speedstep_processor,
-				     &speedstep_freqs[SPEEDSTEP_LOW].frequency,
-				     &speedstep_freqs[SPEEDSTEP_HIGH].frequency,
-				     &policy->cpuinfo.transition_latency,
-				     &speedstep_set_state);
-	set_cpus_allowed_ptr(current, &cpus_allowed);
-	if (result)
-		return result;
+	gf.policy = policy;
+	smp_call_function_single(policy_cpu, get_freqs_on_cpu, &gf, 1);
+	if (gf.ret)
+		return gf.ret;
 
 	/* get current speed setting */
-	speed = _speedstep_get(policy->cpus);
+	speed = speedstep_get(policy_cpu);
 	if (!speed)
 		return -EIO;
 

arch/x86/kernel/cpu/cpufreq/speedstep-lib.c

@@ -226,6 +226,7 @@ static unsigned int pentium4_get_frequency(void)
 }
 
 
+/* Warning: may get called from smp_call_function_single. */
 unsigned int speedstep_get_frequency(unsigned int processor)
 {
 	switch (processor) {