[V4,1/3] cpufreq: Fix locking issues with governors

Message ID fdc55a7550a6a6a95dab1c80ff94d461b8ba0664.1593418662.git.viresh.kumar@linaro.org
State Accepted
Commit 8cc46ae565c393f77417cb9530b1265eb50f5d2e
Headers show
Series
  • cpufreq: Allow default governor on cmdline and fix locking issues
Related show

Commit Message

Viresh Kumar June 29, 2020, 8:24 a.m.
The locking around governors handling isn't adequate currently. The list
of governors should never be traversed without locking in place. Also we
must make sure the governor isn't removed while it is still referenced
by code.

Reported-by: Quentin Perret <qperret@google.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

---
 drivers/cpufreq/cpufreq.c | 58 +++++++++++++++++++++++----------------
 1 file changed, 35 insertions(+), 23 deletions(-)

-- 
2.25.0.rc1.19.g042ed3e048af

Comments

Quentin Perret June 29, 2020, 9:37 a.m. | #1
On Monday 29 Jun 2020 at 13:54:58 (+0530), Viresh Kumar wrote:
> The locking around governors handling isn't adequate currently. The list
> of governors should never be traversed without locking in place. Also we
> must make sure the governor isn't removed while it is still referenced
> by code.
> 
> Reported-by: Quentin Perret <qperret@google.com>

Reviewed-by: Quentin Perret <qperret@google.com>

Thanks!
Quentin

Patch

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 0128de3603df..e9e8200a0211 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -621,6 +621,24 @@  static struct cpufreq_governor *find_governor(const char *str_governor)
 	return NULL;
 }
 
+static struct cpufreq_governor *get_governor(const char *str_governor)
+{
+	struct cpufreq_governor *t;
+
+	mutex_lock(&cpufreq_governor_mutex);
+	t = find_governor(str_governor);
+	if (!t)
+		goto unlock;
+
+	if (!try_module_get(t->owner))
+		t = NULL;
+
+unlock:
+	mutex_unlock(&cpufreq_governor_mutex);
+
+	return t;
+}
+
 static unsigned int cpufreq_parse_policy(char *str_governor)
 {
 	if (!strncasecmp(str_governor, "performance", CPUFREQ_NAME_LEN))
@@ -640,28 +658,14 @@  static struct cpufreq_governor *cpufreq_parse_governor(char *str_governor)
 {
 	struct cpufreq_governor *t;
 
-	mutex_lock(&cpufreq_governor_mutex);
-
-	t = find_governor(str_governor);
-	if (!t) {
-		int ret;
-
-		mutex_unlock(&cpufreq_governor_mutex);
-
-		ret = request_module("cpufreq_%s", str_governor);
-		if (ret)
-			return NULL;
-
-		mutex_lock(&cpufreq_governor_mutex);
+	t = get_governor(str_governor);
+	if (t)
+		return t;
 
-		t = find_governor(str_governor);
-	}
-	if (t && !try_module_get(t->owner))
-		t = NULL;
-
-	mutex_unlock(&cpufreq_governor_mutex);
+	if (request_module("cpufreq_%s", str_governor))
+		return NULL;
 
-	return t;
+	return get_governor(str_governor);
 }
 
 /**
@@ -815,12 +819,14 @@  static ssize_t show_scaling_available_governors(struct cpufreq_policy *policy,
 		goto out;
 	}
 
+	mutex_lock(&cpufreq_governor_mutex);
 	for_each_governor(t) {
 		if (i >= (ssize_t) ((PAGE_SIZE / sizeof(char))
 		    - (CPUFREQ_NAME_LEN + 2)))
-			goto out;
+			break;
 		i += scnprintf(&buf[i], CPUFREQ_NAME_PLEN, "%s ", t->name);
 	}
+	mutex_unlock(&cpufreq_governor_mutex);
 out:
 	i += sprintf(&buf[i], "\n");
 	return i;
@@ -1058,15 +1064,17 @@  static int cpufreq_init_policy(struct cpufreq_policy *policy)
 	struct cpufreq_governor *def_gov = cpufreq_default_governor();
 	struct cpufreq_governor *gov = NULL;
 	unsigned int pol = CPUFREQ_POLICY_UNKNOWN;
+	int ret;
 
 	if (has_target()) {
 		/* Update policy governor to the one used before hotplug. */
-		gov = find_governor(policy->last_governor);
+		gov = get_governor(policy->last_governor);
 		if (gov) {
 			pr_debug("Restoring governor %s for cpu %d\n",
 				 policy->governor->name, policy->cpu);
 		} else if (def_gov) {
 			gov = def_gov;
+			__module_get(gov->owner);
 		} else {
 			return -ENODATA;
 		}
@@ -1089,7 +1097,11 @@  static int cpufreq_init_policy(struct cpufreq_policy *policy)
 			return -ENODATA;
 	}
 
-	return cpufreq_set_policy(policy, gov, pol);
+	ret = cpufreq_set_policy(policy, gov, pol);
+	if (gov)
+		module_put(gov->owner);
+
+	return ret;
 }
 
 static int cpufreq_add_policy_cpu(struct cpufreq_policy *policy, unsigned int cpu)