linux-kernel - [PATCH v6 1/2] cpufreq: Abort show/store for half initialized policy

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Date:   Mon, 16 May 2022 10:44:47 +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 v6 1/2] cpufreq: Abort show/store for half initialized policy

If policy initialization fails after the sysfs files are created,
there is a possibility that we may end up running show()/store()
callbacks for half initialized policies, which may have unpredictable
outcomes.

Abort show/store in such a case by making sure the policy is active.
Also inactivate the policy on such failures.

Signed-off-by: Schspa Shi <schspa@...il.com>

---

Changelog:
v1 -> v2:
        - Fix bad critical region enlarge which causes uninitialized
          unlock.
        - Move cpumask_clear(policy->cpus); before out_offline_policy
v2 -> v3:
        - Remove the missed down_write() before
          cpumask_and(policy->cpus, policy->cpus, cpu_online_mask);
v3 -> v4:
        - Seprate to two patchs.
        - Add policy_is_inactive check before sysfs access
v4 -> v5:
        - Change the commit message as Viresh advised.
        - Initialize ret to -EBUSY to get rid of the else part.
---
 drivers/cpufreq/cpufreq.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 80f535cc8a75..ba73be6f0490 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -947,13 +947,14 @@ static ssize_t show(struct kobject *kobj, struct attribute *attr, char *buf)
 {
 	struct cpufreq_policy *policy = to_policy(kobj);
 	struct freq_attr *fattr = to_attr(attr);
-	ssize_t ret;
+	ssize_t ret = -EBUSY;
 
 	if (!fattr->show)
 		return -EIO;
 
 	down_read(&policy->rwsem);
-	ret = fattr->show(policy, buf);
+	if (likely(!policy_is_inactive(policy)))
+		ret = fattr->show(policy, buf);
 	up_read(&policy->rwsem);
 
 	return ret;
@@ -964,7 +965,7 @@ static ssize_t store(struct kobject *kobj, struct attribute *attr,
 {
 	struct cpufreq_policy *policy = to_policy(kobj);
 	struct freq_attr *fattr = to_attr(attr);
-	ssize_t ret = -EINVAL;
+	ssize_t ret = -EBUSY;
 
 	if (!fattr->store)
 		return -EIO;
@@ -978,7 +979,8 @@ static ssize_t store(struct kobject *kobj, struct attribute *attr,
 
 	if (cpu_online(policy->cpu)) {
 		down_write(&policy->rwsem);
-		ret = fattr->store(policy, buf, count);
+		if (likely(!policy_is_inactive(policy)))
+			ret = fattr->store(policy, buf, count);
 		up_write(&policy->rwsem);
 	}
 
@@ -1533,6 +1535,7 @@ static int cpufreq_online(unsigned int cpu)
 	for_each_cpu(j, policy->real_cpus)
 		remove_cpu_dev_symlink(policy, get_cpu_device(j));
 
+	cpumask_clear(policy->cpus);
 	up_write(&policy->rwsem);
 
 out_offline_policy:
-- 
2.29.0