[PATCH v2 6/6] devfreq: Get module refcount in try_then_request_governor()

[Jie Zhan <zhanjie9@hisilicon.com>]

Get a refcount of the governor module in try_then_request_governor() so
that the governor module cannot be unloaded between finding the governor
and the caller using it.

Signed-off-by: Jie Zhan <zhanjie9@hisilicon.com>
---
 drivers/devfreq/devfreq.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index 2ea42325d030..fb1a7aa168aa 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -285,6 +285,9 @@ static struct devfreq_governor *find_devfreq_governor(const char *name)
  * and the driver that call devfreq_add_device) are built as modules.
  * devfreq_list_lock should be held by the caller. Returns the matched
  * governor's pointer or an error pointer.
+ * On success, this holds a refcount of the governor module to prevent the
+ * module from being unloaded during usage, so the caller should put a module
+ * refcount after using it.
  */
 static struct devfreq_governor *try_then_request_governor(const char *name)
 {
@@ -313,8 +316,13 @@ static struct devfreq_governor *try_then_request_governor(const char *name)
 			return (err < 0) ? ERR_PTR(err) : ERR_PTR(-EINVAL);
 
 		governor = find_devfreq_governor(name);
+		if (IS_ERR(governor))
+			return governor;
 	}
 
+	if (!try_module_get(governor->owner))
+		return ERR_PTR(-EBUSY);
+
 	return governor;
 }
 
@@ -1009,6 +1017,7 @@ struct devfreq *devfreq_add_device(struct device *dev,
 	}
 
 	err = devfreq_set_governor(devfreq, governor);
+	module_put(governor->owner);
 	if (err) {
 		dev_err_probe(dev, err,
 			"%s: Unable to start governor for the device\n",
@@ -1446,6 +1455,7 @@ static ssize_t governor_store(struct device *dev, struct device_attribute *attr,
 		return PTR_ERR(governor);
 
 	ret = devfreq_set_governor(df, governor);
+	module_put(governor->owner);
 	if (ret)
 		return ret;
 
-- 
2.43.0