linux-kernel - [PATCH] opp: Reinitialize the list_kref before adding the static OPPs again

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Date:   Fri, 18 Oct 2019 14:58:41 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>, linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Dmitry Osipenko <digetx@...il.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] opp: Reinitialize the list_kref before adding the static OPPs again

The list_kref reaches a count of 0 when all the static OPPs are removed,
for example when dev_pm_opp_of_cpumask_remove_table() is called, though
the actual OPP table may not get freed as it may still be referenced by
other parts of the kernel, like from a call to
dev_pm_opp_set_supported_hw(). And if we call
dev_pm_opp_of_cpumask_add_table() again at this point, we must
reinitialize the list_kref otherwise the kernel will hit a WARN() in
kref infrastructure for incrementing a kref with value 0.

Fixes: 11e1a1648298 ("opp: Don't decrement uninitialized list_kref")
Reported-by: Dmitry Osipenko <digetx@...il.com>
Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
---
 drivers/opp/of.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/opp/of.c b/drivers/opp/of.c
index 6dc41faf74b5..1cbb58240b80 100644
--- a/drivers/opp/of.c
+++ b/drivers/opp/of.c
@@ -663,6 +663,13 @@ static int _of_add_opp_table_v2(struct device *dev, struct opp_table *opp_table)
 		return 0;
 	}
 
+	/*
+	 * Re-initialize list_kref every time we add static OPPs to the OPP
+	 * table as the reference count may be 0 after the last tie static OPPs
+	 * were removed.
+	 */
+	kref_init(&opp_table->list_kref);
+
 	/* We have opp-table node now, iterate over it and add OPPs */
 	for_each_available_child_of_node(opp_table->np, np) {
 		opp = _opp_add_static_v2(opp_table, dev, np);
-- 
2.21.0.rc0.269.g1a574e7a288b