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Message-ID: <7191200.L2L3Fy8tSf@vostro.rjw.lan>
Date: Wed, 16 Nov 2016 03:38:40 +0100
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Linux PM list <linux-pm@...r.kernel.org>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Viresh Kumar <viresh.kumar@...aro.org>,
Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: [PATCH v2] cpufreq: Avoid a couple of races related to cpufreq_cpu_get()
From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
The cpumask_test_cpu() check in cpufreq_cpu_get_raw() is sort of
pointless, because it may be racy with respect to CPU online/offline
which sets/clears the policy->cpus mask.
Some of the races resulting from that are benign (worst case, stale
values may be returned from some sysfs attribute for a relatively
short period), but some of them may lead to invocations of low-level
cpufreq driver callbacks for offline CPUs which is not guaranteed to
work in general.
For this reason, move the cpumask_test_cpu() check away from
cpufreq_cpu_get_raw() and reserve it for the ondemand governor,
which calls it for online CPUs only and with CPU online/offline
locked anyway, and make the other callers of it use the per-CPU
variable whose value is returned by it directly.
With that, add the cpumask_test_cpu() check to cpufreq_generic_get()
to preserve its current behavior for offline CPUs and to the callers
of cpufreq_cpu_get(). There, in the cases when the races might
lead to invocations of driver callbacks for offline CPUs, put it
under policy->rwsem.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
-> v2:
* Modify the changelog to make it better explain what's going on.
* Add the missing cpumask_test_cpu() check to cpufreq_offline().
---
drivers/cpufreq/cpufreq.c | 52 ++++++++++++++++++++++++++++++++--------------
1 file changed, 37 insertions(+), 15 deletions(-)
Index: linux-pm/drivers/cpufreq/cpufreq.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/cpufreq.c
+++ linux-pm/drivers/cpufreq/cpufreq.c
@@ -65,6 +65,12 @@ static struct cpufreq_driver *cpufreq_dr
static DEFINE_PER_CPU(struct cpufreq_policy *, cpufreq_cpu_data);
static DEFINE_RWLOCK(cpufreq_driver_lock);
+struct cpufreq_policy *cpufreq_cpu_get_raw(unsigned int cpu)
+{
+ return per_cpu(cpufreq_cpu_data, cpu);
+}
+EXPORT_SYMBOL_GPL(cpufreq_cpu_get_raw);
+
/* Flag to suspend/resume CPUFreq governors */
static bool cpufreq_suspended;
@@ -192,19 +198,12 @@ int cpufreq_generic_init(struct cpufreq_
}
EXPORT_SYMBOL_GPL(cpufreq_generic_init);
-struct cpufreq_policy *cpufreq_cpu_get_raw(unsigned int cpu)
-{
- struct cpufreq_policy *policy = per_cpu(cpufreq_cpu_data, cpu);
-
- return policy && cpumask_test_cpu(cpu, policy->cpus) ? policy : NULL;
-}
-EXPORT_SYMBOL_GPL(cpufreq_cpu_get_raw);
-
unsigned int cpufreq_generic_get(unsigned int cpu)
{
- struct cpufreq_policy *policy = cpufreq_cpu_get_raw(cpu);
+ struct cpufreq_policy *policy = per_cpu(cpufreq_cpu_data, cpu);
- if (!policy || IS_ERR(policy->clk)) {
+ if (!policy || !cpumask_test_cpu(cpu, policy->cpus) ||
+ IS_ERR(policy->clk)) {
pr_err("%s: No %s associated to cpu: %d\n",
__func__, policy ? "clk" : "policy", cpu);
return 0;
@@ -240,7 +239,7 @@ struct cpufreq_policy *cpufreq_cpu_get(u
if (cpufreq_driver) {
/* get the CPU */
- policy = cpufreq_cpu_get_raw(cpu);
+ policy = per_cpu(cpufreq_cpu_data, cpu);
if (policy)
kobject_get(&policy->kobj);
}
@@ -1328,13 +1327,19 @@ static int cpufreq_offline(unsigned int
pr_debug("%s: unregistering CPU %u\n", __func__, cpu);
- policy = cpufreq_cpu_get_raw(cpu);
+ policy = per_cpu(cpufreq_cpu_data, cpu);
if (!policy) {
pr_debug("%s: No cpu_data found\n", __func__);
return 0;
}
down_write(&policy->rwsem);
+
+ if (!cpumask_test_cpu(cpu, policy->cpus)) {
+ pr_debug("%s: CPU %u is offline\n", __func__, cpu);
+ goto unlock;
+ }
+
if (has_target())
cpufreq_stop_governor(policy);
@@ -1455,7 +1460,9 @@ unsigned int cpufreq_quick_get(unsigned
policy = cpufreq_cpu_get(cpu);
if (policy) {
- ret_freq = policy->cur;
+ if (cpumask_test_cpu(cpu, policy->cpus))
+ ret_freq = policy->cur;
+
cpufreq_cpu_put(policy);
}
@@ -1475,7 +1482,9 @@ unsigned int cpufreq_quick_get_max(unsig
unsigned int ret_freq = 0;
if (policy) {
- ret_freq = policy->max;
+ if (cpumask_test_cpu(cpu, policy->cpus))
+ ret_freq = policy->max;
+
cpufreq_cpu_put(policy);
}
@@ -1526,7 +1535,10 @@ unsigned int cpufreq_get(unsigned int cp
if (policy) {
down_read(&policy->rwsem);
- ret_freq = __cpufreq_get(policy);
+
+ if (cpumask_test_cpu(cpu, policy->cpus))
+ ret_freq = __cpufreq_get(policy);
+
up_read(&policy->rwsem);
cpufreq_cpu_put(policy);
@@ -2142,6 +2154,11 @@ int cpufreq_get_policy(struct cpufreq_po
if (!cpu_policy)
return -EINVAL;
+ if (!cpumask_test_cpu(cpu, policy->cpus)) {
+ cpufreq_cpu_put(cpu_policy);
+ return -EINVAL;
+ }
+
memcpy(policy, cpu_policy, sizeof(*policy));
cpufreq_cpu_put(cpu_policy);
@@ -2265,6 +2282,11 @@ int cpufreq_update_policy(unsigned int c
down_write(&policy->rwsem);
+ if (!cpumask_test_cpu(cpu, policy->cpus)) {
+ ret = -ENODEV;
+ goto unlock;
+ }
+
pr_debug("updating policy for CPU %u\n", cpu);
memcpy(&new_policy, policy, sizeof(*policy));
new_policy.min = policy->user_policy.min;
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