Subject: [PATCH v2 3/5] OPP: Allow notifiers to call dev_pm_opp_get_{voltage, freq} RCU-free

From: [email-masked] (Stephen Boyd)
Date: Fri, 18 Sep 2015 17:52:07 -0700

We pass the dev_pm_opp structure to OPP notifiers but the users
of the notifier need to surround calls to dev_pm_opp_get_*() with
RCU read locks to avoid lockdep warnings. The notifier is already
called with the dev_opp's srcu lock held, so it should be safe to
assume the devm_pm_opp structure is already protected inside the
notifier. Update the lockdep check for this.

Cc: Krzysztof Kozlowski <[email-masked]>
Signed-off-by: Stephen Boyd <[email-masked]>
---
 drivers/base/power/opp.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/drivers/base/power/opp.c b/drivers/base/power/opp.c
index 35b66c46dcb7..1d8c45e53245 100644
--- a/drivers/base/power/opp.c
+++ b/drivers/base/power/opp.c
@@ -146,9 +146,10 @@ static LIST_HEAD(dev_opp_list);
 /* Lock to allow exclusive modification to the device and opp lists */
 static DEFINE_MUTEX(dev_opp_list_lock);
 
-#define opp_rcu_lockdep_assert()					\
+#define opp_rcu_lockdep_assert(s)					\
 do {									\
 	RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&			\
+				!(s && srcu_read_lock_held(s)) &&	\
 				!lockdep_is_held(&dev_opp_list_lock),	\
 			   "Missing rcu_read_lock() or "		\
 			   "dev_opp_list_lock protection");		\
@@ -236,9 +237,10 @@ unsigned long dev_pm_opp_get_voltage(struct dev_pm_opp *opp)
 	struct dev_pm_opp *tmp_opp;
 	unsigned long v = 0;
 
-	opp_rcu_lockdep_assert();
+	opp_rcu_lockdep_assert(&opp->dev_opp->srcu_head.srcu);
 
-	tmp_opp = rcu_dereference(opp);
+	tmp_opp = srcu_dereference_check(opp, &opp->dev_opp->srcu_head.srcu,
+					 rcu_read_lock_held());
 	if (IS_ERR_OR_NULL(tmp_opp) || !tmp_opp->available)
 		pr_err("%s: Invalid parameters\n", __func__);
 	else
@@ -268,9 +270,10 @@ unsigned long dev_pm_opp_get_freq(struct dev_pm_opp *opp)
 	struct dev_pm_opp *tmp_opp;
 	unsigned long f = 0;
 
-	opp_rcu_lockdep_assert();
+	opp_rcu_lockdep_assert(&opp->dev_opp->srcu_head.srcu);
 
-	tmp_opp = rcu_dereference(opp);
+	tmp_opp = srcu_dereference_check(opp, &opp->dev_opp->srcu_head.srcu,
+					 rcu_read_lock_held());
 	if (IS_ERR_OR_NULL(tmp_opp) || !tmp_opp->available)
 		pr_err("%s: Invalid parameters\n", __func__);
 	else
@@ -437,7 +440,7 @@ struct dev_pm_opp *dev_pm_opp_find_freq_exact(struct device *dev,
 	struct device_opp *dev_opp;
 	struct dev_pm_opp *temp_opp, *opp = ERR_PTR(-ERANGE);
 
-	opp_rcu_lockdep_assert();
+	opp_rcu_lockdep_assert(NULL);
 
 	dev_opp = _find_device_opp(dev);
 	if (IS_ERR(dev_opp)) {
@@ -485,7 +488,7 @@ struct dev_pm_opp *dev_pm_opp_find_freq_ceil(struct device *dev,
 	struct device_opp *dev_opp;
 	struct dev_pm_opp *temp_opp, *opp = ERR_PTR(-ERANGE);
 
-	opp_rcu_lockdep_assert();
+	opp_rcu_lockdep_assert(NULL);
 
 	if (!dev || !freq) {
 		dev_err(dev, "%s: Invalid argument freq=%p\n", __func__, freq);
@@ -535,7 +538,7 @@ struct dev_pm_opp *dev_pm_opp_find_freq_floor(struct device *dev,
 	struct device_opp *dev_opp;
 	struct dev_pm_opp *temp_opp, *opp = ERR_PTR(-ERANGE);
 
-	opp_rcu_lockdep_assert();
+	opp_rcu_lockdep_assert(NULL);
 
 	if (!dev || !freq) {
 		dev_err(dev, "%s: Invalid argument freq=%p\n", __func__, freq);
-- 
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