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From:   Viresh Kumar <viresh.kumar@linaro.org>
To:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Viresh Kumar <viresh.kumar@linaro.org>
Cc:     linux-pm@vger.kernel.org,
        Vincent Guittot <vincent.guittot@linaro.org>,
        kernel test robot <oliver.sang@intel.com>,
        linux-kernel@vger.kernel.org
Subject: [PATCH V2 2/3] cpufreq: Panic if policy is active in cpufreq_policy_free()
Date:   Fri, 27 May 2022 09:23:34 +0530
Message-Id: <426bf6edc80b2e944d459fa7b8dffbe8b73bb3d9.1653623526.git.viresh.kumar@linaro.org>
In-Reply-To: <8c3d50faf8811e86136fb3f9c459e43fc3c50bc0.1653565641.git.viresh.kumar@linaro.org>
References: <8c3d50faf8811e86136fb3f9c459e43fc3c50bc0.1653565641.git.viresh.kumar@linaro.org>
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With the new design in place, to avoid potential races show() and
store() callbacks check if the policy is active or not before proceeding
any further. And in order to guarantee that cpufreq_policy_free() must
be called after clearing the policy->cpus mask, i.e. by marking it
inactive.

Lets make sure we don't get a bug around this later and catch this early
by putting a BUG_ON() within cpufreq_policy_free().

Also update cpufreq_online() a bit to make sure we clear the cpus mask
for each error case before calling cpufreq_policy_free().

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
V2: Update cpufreq_online() and changelog.

 drivers/cpufreq/cpufreq.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index e24aa5d4bca5..0f8245731783 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1284,6 +1284,12 @@ static void cpufreq_policy_free(struct cpufreq_policy *policy)
 	unsigned long flags;
 	int cpu;
 
+	/*
+	 * The callers must ensure the policy is inactive by now, to avoid any
+	 * races with show()/store() callbacks.
+	 */
+	BUG_ON(!policy_is_inactive(policy));
+
 	/* Remove policy from list */
 	write_lock_irqsave(&cpufreq_driver_lock, flags);
 	list_del(&policy->policy_list);
@@ -1538,8 +1544,6 @@ static int cpufreq_online(unsigned int cpu)
 	for_each_cpu(j, policy->real_cpus)
 		remove_cpu_dev_symlink(policy, j, get_cpu_device(j));
 
-	cpumask_clear(policy->cpus);
-
 out_offline_policy:
 	if (cpufreq_driver->offline)
 		cpufreq_driver->offline(policy);
@@ -1549,6 +1553,7 @@ static int cpufreq_online(unsigned int cpu)
 		cpufreq_driver->exit(policy);
 
 out_free_policy:
+	cpumask_clear(policy->cpus);
 	up_write(&policy->rwsem);
 
 	cpufreq_policy_free(policy);
-- 
2.31.1.272.g89b43f80a514