devfreq: exynos: Don't use OPP structures outside of RCU locks

The OPP structures are abused to the best here, without understanding
how the OPP core and RCU locks work.

In short, the OPP pointer saved 'struct exynos_bus' can become invalid
under your nose, as the OPP core may free it.

Fix various abuses around OPP structures and calls.
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Chanwoo Choi <cw00.choi@samsung.com>
Tested-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/devfreq/exynos-bus.c

@@ -35,7 +35,7 @@ struct exynos_bus {
 	unsigned int edev_count;
 	struct mutex lock;
 
-	struct dev_pm_opp *curr_opp;
+	unsigned long curr_freq;
 
 	struct regulator *regulator;
 	struct clk *clk;
@@ -99,7 +99,7 @@ static int exynos_bus_target(struct device *dev, unsigned long *freq, u32 flags)
 {
 	struct exynos_bus *bus = dev_get_drvdata(dev);
 	struct dev_pm_opp *new_opp;
-	unsigned long old_freq, new_freq, old_volt, new_volt, tol;
+	unsigned long old_freq, new_freq, new_volt, tol;
 	int ret = 0;
 
 	/* Get new opp-bus instance according to new bus clock */
@@ -113,8 +113,7 @@ static int exynos_bus_target(struct device *dev, unsigned long *freq, u32 flags)
 
 	new_freq = dev_pm_opp_get_freq(new_opp);
 	new_volt = dev_pm_opp_get_voltage(new_opp);
-	old_freq = dev_pm_opp_get_freq(bus->curr_opp);
-	old_volt = dev_pm_opp_get_voltage(bus->curr_opp);
+	old_freq = bus->curr_freq;
 	rcu_read_unlock();
 
 	if (old_freq == new_freq)
@@ -146,7 +145,7 @@ static int exynos_bus_target(struct device *dev, unsigned long *freq, u32 flags)
 			goto out;
 		}
 	}
-	bus->curr_opp = new_opp;
+	bus->curr_freq = new_freq;
 
 	dev_dbg(dev, "Set the frequency of bus (%lukHz -> %lukHz)\n",
 			old_freq/1000, new_freq/1000);
@@ -163,9 +162,7 @@ static int exynos_bus_get_dev_status(struct device *dev,
 	struct devfreq_event_data edata;
 	int ret;
 
-	rcu_read_lock();
-	stat->current_frequency = dev_pm_opp_get_freq(bus->curr_opp);
-	rcu_read_unlock();
+	stat->current_frequency = bus->curr_freq;
 
 	ret = exynos_bus_get_event(bus, &edata);
 	if (ret < 0) {
@@ -226,7 +223,7 @@ static int exynos_bus_passive_target(struct device *dev, unsigned long *freq,
 	}
 
 	new_freq = dev_pm_opp_get_freq(new_opp);
-	old_freq = dev_pm_opp_get_freq(bus->curr_opp);
+	old_freq = bus->curr_freq;
 	rcu_read_unlock();
 
 	if (old_freq == new_freq)
@@ -242,7 +239,7 @@ static int exynos_bus_passive_target(struct device *dev, unsigned long *freq,
 	}
 
 	*freq = new_freq;
-	bus->curr_opp = new_opp;
+	bus->curr_freq = new_freq;
 
 	dev_dbg(dev, "Set the frequency of bus (%lukHz -> %lukHz)\n",
 			old_freq/1000, new_freq/1000);
@@ -335,6 +332,7 @@ static int exynos_bus_parse_of(struct device_node *np,
 			      struct exynos_bus *bus)
 {
 	struct device *dev = bus->dev;
+	struct dev_pm_opp *opp;
 	unsigned long rate;
 	int ret;
 
@@ -352,22 +350,23 @@ static int exynos_bus_parse_of(struct device_node *np,
 	}
 
 	/* Get the freq and voltage from OPP table to scale the bus freq */
-	rcu_read_lock();
 	ret = dev_pm_opp_of_add_table(dev);
 	if (ret < 0) {
 		dev_err(dev, "failed to get OPP table\n");
-		rcu_read_unlock();
 		goto err_clk;
 	}
 
 	rate = clk_get_rate(bus->clk);
-	bus->curr_opp = devfreq_recommended_opp(dev, &rate, 0);
-	if (IS_ERR(bus->curr_opp)) {
+
+	rcu_read_lock();
+	opp = devfreq_recommended_opp(dev, &rate, 0);
+	if (IS_ERR(opp)) {
 		dev_err(dev, "failed to find dev_pm_opp\n");
 		rcu_read_unlock();
-		ret = PTR_ERR(bus->curr_opp);
+		ret = PTR_ERR(opp);
 		goto err_opp;
 	}
+	bus->curr_freq = dev_pm_opp_get_freq(opp);
 	rcu_read_unlock();
 
 	return 0;