OPP: Protect dev_list with opp_table lock

The dev_list needs to be protected with a lock, else we may have
simultaneous access (addition/removal) to it and that would be racy.
Extend scope of the opp_table lock to protect dev_list as well.
Tested-by: Niklas Cassel <niklas.cassel@linaro.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

drivers/opp/core.c

@@ -48,9 +48,14 @@ static struct opp_device *_find_opp_dev(const struct device *dev,
 static struct opp_table *_find_opp_table_unlocked(struct device *dev)
 {
 	struct opp_table *opp_table;
+	bool found;
 
 	list_for_each_entry(opp_table, &opp_tables, node) {
-		if (_find_opp_dev(dev, opp_table)) {
+		mutex_lock(&opp_table->lock);
+		found = !!_find_opp_dev(dev, opp_table);
+		mutex_unlock(&opp_table->lock);
+
+		if (found) {
 			_get_opp_table_kref(opp_table);
 
 			return opp_table;
@@ -766,6 +771,8 @@ struct opp_device *_add_opp_dev(const struct device *dev,
 
 	/* Initialize opp-dev */
 	opp_dev->dev = dev;
+
+	mutex_lock(&opp_table->lock);
 	list_add(&opp_dev->node, &opp_table->dev_list);
 
 	/* Create debugfs entries for the opp_table */
@@ -773,6 +780,7 @@ struct opp_device *_add_opp_dev(const struct device *dev,
 	if (ret)
 		dev_err(dev, "%s: Failed to register opp debugfs (%d)\n",
 			__func__, ret);
+	mutex_unlock(&opp_table->lock);
 
 	return opp_dev;
 }
@@ -791,6 +799,7 @@ static struct opp_table *_allocate_opp_table(struct device *dev)
 	if (!opp_table)
 		return NULL;
 
+	mutex_init(&opp_table->lock);
 	INIT_LIST_HEAD(&opp_table->dev_list);
 
 	opp_dev = _add_opp_dev(dev, opp_table);
@@ -812,7 +821,6 @@ static struct opp_table *_allocate_opp_table(struct device *dev)
 
 	BLOCKING_INIT_NOTIFIER_HEAD(&opp_table->head);
 	INIT_LIST_HEAD(&opp_table->opp_list);
-	mutex_init(&opp_table->lock);
 	kref_init(&opp_table->kref);
 
 	/* Secure the device table modification */
@@ -854,6 +862,10 @@ static void _opp_table_kref_release(struct kref *kref)
 	if (!IS_ERR(opp_table->clk))
 		clk_put(opp_table->clk);
 
+	/*
+	 * No need to take opp_table->lock here as we are guaranteed that no
+	 * references to the OPP table are taken at this point.
+	 */
 	opp_dev = list_first_entry(&opp_table->dev_list, struct opp_device,
 				   node);
 
@@ -1716,6 +1728,9 @@ void _dev_pm_opp_remove_table(struct opp_table *opp_table, struct device *dev,
 {
 	struct dev_pm_opp *opp, *tmp;
 
+	/* Protect dev_list */
+	mutex_lock(&opp_table->lock);
+
 	/* Find if opp_table manages a single device */
 	if (list_is_singular(&opp_table->dev_list)) {
 		/* Free static OPPs */
@@ -1733,6 +1748,8 @@ void _dev_pm_opp_remove_table(struct opp_table *opp_table, struct device *dev,
 	} else {
 		_remove_opp_dev(_find_opp_dev(dev, opp_table), opp_table);
 	}
+
+	mutex_unlock(&opp_table->lock);
 }
 
 void _dev_pm_opp_find_and_remove_table(struct device *dev, bool remove_all)

drivers/opp/cpu.c

@@ -226,8 +226,10 @@ int dev_pm_opp_get_sharing_cpus(struct device *cpu_dev, struct cpumask *cpumask)
 	cpumask_clear(cpumask);
 
 	if (opp_table->shared_opp == OPP_TABLE_ACCESS_SHARED) {
+		mutex_lock(&opp_table->lock);
 		list_for_each_entry(opp_dev, &opp_table->dev_list, node)
 			cpumask_set_cpu(opp_dev->dev->id, cpumask);
+		mutex_unlock(&opp_table->lock);
 	} else {
 		cpumask_set_cpu(cpu_dev->id, cpumask);
 	}

drivers/opp/opp.h

@@ -126,7 +126,7 @@ enum opp_table_access {
  * @dev_list:	list of devices that share these OPPs
  * @opp_list:	table of opps
  * @kref:	for reference count of the table.
- * @lock:	mutex protecting the opp_list.
+ * @lock:	mutex protecting the opp_list and dev_list.
  * @np:		struct device_node pointer for opp's DT node.
  * @clock_latency_ns_max: Max clock latency in nanoseconds.
  * @shared_opp: OPP is shared between multiple devices.