linux-kernel - [PATCH v5 2/2] cpufreq: make interface functions and lock holding state clear

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Date:   Fri, 13 May 2022 19:08:48 +0800
From:   Schspa Shi <schspa@...il.com>
To:     rafael@...nel.org, viresh.kumar@...aro.org
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        schspa@...il.com
Subject: [PATCH v5 2/2] cpufreq: make interface functions and lock holding state clear

cpufreq_offline() calls offline() and exit() under the policy rwsem
But they are called outside the rwsem in cpufreq_online().

This patch move the offline(), exit(), online(), init() to be inside
of policy rwsem to achieve a clear lock relationship.

All the init() online() implement only initialize policy object without
holding this lock and won't call cpufreq APIs need to hold this lock.

Signed-off-by: Schspa Shi <schspa@...il.com>
---
 drivers/cpufreq/cpufreq.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index ba73be6f0490..0f0f202f9a05 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1339,12 +1339,12 @@ static int cpufreq_online(unsigned int cpu)
 		down_write(&policy->rwsem);
 		policy->cpu = cpu;
 		policy->governor = NULL;
-		up_write(&policy->rwsem);
 	} else {
 		new_policy = true;
 		policy = cpufreq_policy_alloc(cpu);
 		if (!policy)
 			return -ENOMEM;
+		down_write(&policy->rwsem);
 	}
 
 	if (!new_policy && cpufreq_driver->online) {
@@ -1384,7 +1384,6 @@ static int cpufreq_online(unsigned int cpu)
 		cpumask_copy(policy->related_cpus, policy->cpus);
 	}
 
-	down_write(&policy->rwsem);
 	/*
 	 * affected cpus must always be the one, which are online. We aren't
 	 * managing offline cpus here.
@@ -1536,7 +1535,6 @@ static int cpufreq_online(unsigned int cpu)
 		remove_cpu_dev_symlink(policy, get_cpu_device(j));
 
 	cpumask_clear(policy->cpus);
-	up_write(&policy->rwsem);
 
 out_offline_policy:
 	if (cpufreq_driver->offline)
@@ -1545,6 +1543,7 @@ static int cpufreq_online(unsigned int cpu)
 out_exit_policy:
 	if (cpufreq_driver->exit)
 		cpufreq_driver->exit(policy);
+	up_write(&policy->rwsem);
 
 out_free_policy:
 	cpufreq_policy_free(policy);
-- 
2.29.0