diff mbox series

[V2] PM / OPP: Call notifier without holding opp_table->lock

Message ID 5b70f7bdf12975f869a83f77e36bf3a40e0fa4b9.1505939072.git.viresh.kumar@linaro.org
State Accepted
Commit e4d8ae00169f7686e1da5a62e5cf797d12bf8822
Headers show
Series [V2] PM / OPP: Call notifier without holding opp_table->lock | expand

Commit Message

Viresh Kumar Sept. 20, 2017, 8:25 p.m. UTC 
The notifier callbacks may want to call some OPP helper routines which
may try to take the same opp_table->lock again and cause a deadlock. One
such usecase was reported by Chanwoo Choi, where calling
dev_pm_opp_disable() leads us to the devfreq's OPP notifier handler,
which further calls dev_pm_opp_find_freq_floor() and it deadlocks.

We don't really need the opp_table->lock to be held across the notifier
call though, all we want to make sure is that the 'opp' doesn't get
freed while being used from within the notifier chain. We can do it with
help of dev_pm_opp_get/put() as well. Let's do it.

Reported-by: Chanwoo Choi <cw00.choi@samsung.com>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

---
V1->V2:
- s/Lets/Let's/ in commit log and added Stephen's tag.

 drivers/base/power/opp/core.c | 7 +++++++
 1 file changed, 7 insertions(+)

-- 
2.7.4
diff mbox series

Patch

diff --git a/drivers/base/power/opp/core.c b/drivers/base/power/opp/core.c
index 4360b4efcd4c..668fd940d362 100644
--- a/drivers/base/power/opp/core.c
+++ b/drivers/base/power/opp/core.c
@@ -1627,6 +1627,9 @@  static int _opp_set_availability(struct device *dev, unsigned long freq,
 
 	opp->available = availability_req;
 
+	dev_pm_opp_get(opp);
+	mutex_unlock(&opp_table->lock);
+
 	/* Notify the change of the OPP availability */
 	if (availability_req)
 		blocking_notifier_call_chain(&opp_table->head, OPP_EVENT_ENABLE,
@@ -1635,8 +1638,12 @@  static int _opp_set_availability(struct device *dev, unsigned long freq,
 		blocking_notifier_call_chain(&opp_table->head,
 					     OPP_EVENT_DISABLE, opp);
 
+	dev_pm_opp_put(opp);
+	goto put_table;
+
 unlock:
 	mutex_unlock(&opp_table->lock);
+put_table:
 	dev_pm_opp_put_opp_table(opp_table);
 	return r;
 }