linux-kernel - [PATCH v2] PM / devfreq: Restart previous governor if new governor fails to start

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Date:   Tue, 25 Oct 2016 18:25:59 -0700
From:   Saravana Kannan <skannan@...eaurora.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Saravana Kannan <skannan@...eaurora.org>
Subject: [PATCH v2] PM / devfreq: Restart previous governor if new governor fails to start

If the new governor fails to start, switch back to old governor so that the
devfreq state is not left in some weird limbo.

Signed-off-by: Saravana Kannan <skannan@...eaurora.org>
---
* Fixed typo in commit text
* Fixed potential NULL deref

 drivers/devfreq/devfreq.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index bf3ea76..243253e 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -919,7 +919,7 @@ static ssize_t governor_store(struct device *dev, struct device_attribute *attr,
 	struct devfreq *df = to_devfreq(dev);
 	int ret;
 	char str_governor[DEVFREQ_NAME_LEN + 1];
-	struct devfreq_governor *governor;
+	const struct devfreq_governor *governor, *prev_gov;
 
 	ret = sscanf(buf, "%" __stringify(DEVFREQ_NAME_LEN) "s", str_governor);
 	if (ret != 1)
@@ -944,12 +944,17 @@ static ssize_t governor_store(struct device *dev, struct device_attribute *attr,
 			goto out;
 		}
 	}
+	prev_gov = df->governor;
 	df->governor = governor;
 	strncpy(df->governor_name, governor->name, DEVFREQ_NAME_LEN);
 	ret = df->governor->event_handler(df, DEVFREQ_GOV_START, NULL);
-	if (ret)
+	if (ret) {
 		dev_warn(dev, "%s: Governor %s not started(%d)\n",
 			 __func__, df->governor->name, ret);
+		df->governor = prev_gov;
+		strncpy(df->governor_name, prev_gov->name, DEVFREQ_NAME_LEN);
+		df->governor->event_handler(df, DEVFREQ_GOV_START, NULL);
+	}
 out:
 	mutex_unlock(&devfreq_list_lock);
 
-- 
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