linux-kernel - [PATCH] cpufreq: Avoid using inactive policies

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Message-ID: <2600582.kqN5q7nCq0@vostro.rjw.lan>
Date:   Thu, 17 Nov 2016 16:08:25 +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] cpufreq: Avoid using inactive policies

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

There are two places in the cpufreq core in which low-level driver
callbacks may be invoked for an inactive cpufreq policy, which isn't
guaranteed to work in general.  Both are due to possible races with
CPU offline.

First, in cpufreq_get(), the policy may become inactive after
the check against policy->cpus in cpufreq_cpu_get() and before
policy->rwsem is acquired, in which case using the policy going
forward may not be correct.

Second, an analogous situation is possible in cpufreq_update_policy().

Avoid using inactive policies by adding policy_is_inactive() checks
to the code in the above places.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/cpufreq/cpufreq.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

Index: linux-pm/drivers/cpufreq/cpufreq.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/cpufreq.c
+++ linux-pm/drivers/cpufreq/cpufreq.c
@@ -1526,7 +1526,10 @@ unsigned int cpufreq_get(unsigned int cp

 	if (policy) {
 		down_read(&policy->rwsem);
-		ret_freq = __cpufreq_get(policy);
+
+		if (!policy_is_inactive(policy))
+			ret_freq = __cpufreq_get(policy);
+
 		up_read(&policy->rwsem);

 		cpufreq_cpu_put(policy);
@@ -2265,6 +2268,9 @@ int cpufreq_update_policy(unsigned int c

 	down_write(&policy->rwsem);

+	if (policy_is_inactive(policy))
+		goto unlock;
+
 	pr_debug("updating policy for CPU %u\n", cpu);
 	memcpy(&new_policy, policy, sizeof(*policy));
 	new_policy.min = policy->user_policy.min;