linux-kernel - [PATCH 4.13 104/110] PM / OPP: Call notifier without holding opp

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Message-Id: <20171003114245.433980820@linuxfoundation.org>
Date:   Tue,  3 Oct 2017 14:30:06 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Chanwoo Choi <cw00.choi@...sung.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: [PATCH 4.13 104/110] PM / OPP: Call notifier without holding opp_table->lock

4.13-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Viresh Kumar <viresh.kumar@...aro.org>

commit e4d8ae00169f7686e1da5a62e5cf797d12bf8822 upstream.

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.

Fixes: 5b650b388844 "PM / OPP: Take kref from _find_opp_table()"
Reported-by: Chanwoo Choi <cw00.choi@...sung.com>
Tested-by: Chanwoo Choi <cw00.choi@...sung.com>
Reviewed-by: Stephen Boyd <sboyd@...eaurora.org>
Reviewed-by: Chanwoo Choi <cw00.choi@...sung.com>
Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- a/drivers/base/power/opp/core.c
+++ b/drivers/base/power/opp/core.c
@@ -1581,6 +1581,9 @@ static int _opp_set_availability(struct

 	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,
@@ -1589,8 +1592,12 @@ static int _opp_set_availability(struct
 		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;
 }