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From:   Dmitry Osipenko <digetx@gmail.com>
To:     Thierry Reding <thierry.reding@gmail.com>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        Georgi Djakov <georgi.djakov@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        Michael Turquette <mturquette@baylibre.com>,
        Stephen Boyd <sboyd@kernel.org>,
        Peter De Schrijver <pdeschrijver@nvidia.com>,
        MyungJoo Ham <myungjoo.ham@samsung.com>,
        Kyungmin Park <kyungmin.park@samsung.com>,
        Chanwoo Choi <cw00.choi@samsung.com>,
        Mikko Perttunen <cyndis@kapsi.fi>,
        Viresh Kumar <vireshk@kernel.org>,
        Peter Geis <pgwipeout@gmail.com>,
        Nicolas Chauvet <kwizart@gmail.com>,
        Krzysztof Kozlowski <krzk@kernel.org>
Cc:     linux-tegra@vger.kernel.org, linux-pm@vger.kernel.org,
        linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
        devicetree@vger.kernel.org
Subject: [PATCH v6 46/52] opp: Put interconnect paths outside of opp_table_lock
Date:   Mon, 26 Oct 2020 01:17:29 +0300
Message-Id: <20201025221735.3062-47-digetx@gmail.com>
In-Reply-To: <20201025221735.3062-1-digetx@gmail.com>
References: <20201025221735.3062-1-digetx@gmail.com>
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This patch fixes lockup which happens when OPP table is released if
interconnect provider uses OPP in the icc_provider->set() callback
and bandwidth of the ICC path is set to 0 by the ICC core when path
is released. The icc_put() doesn't need the opp_table_lock protection,
hence let's move it outside of the lock in order to resolve the problem.

In particular this fixes tegra-devfreq driver lockup on trying to unload
the driver module. The devfreq driver uses OPP-bandwidth API and its ICC
provider also uses OPP for DVFS, hence they both take same opp_table_lock
when OPP table of the devfreq is released.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
---
 drivers/opp/core.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/drivers/opp/core.c b/drivers/opp/core.c
index 2483e765318a..1134df360fe0 100644
--- a/drivers/opp/core.c
+++ b/drivers/opp/core.c
@@ -1187,12 +1187,6 @@ static void _opp_table_kref_release(struct kref *kref)
 	if (!IS_ERR(opp_table->clk))
 		clk_put(opp_table->clk);
 
-	if (opp_table->paths) {
-		for (i = 0; i < opp_table->path_count; i++)
-			icc_put(opp_table->paths[i]);
-		kfree(opp_table->paths);
-	}
-
 	WARN_ON(!list_empty(&opp_table->opp_list));
 
 	list_for_each_entry_safe(opp_dev, temp, &opp_table->dev_list, node) {
@@ -1209,9 +1203,22 @@ static void _opp_table_kref_release(struct kref *kref)
 	mutex_destroy(&opp_table->genpd_virt_dev_lock);
 	mutex_destroy(&opp_table->lock);
 	list_del(&opp_table->node);
-	kfree(opp_table);
 
 	mutex_unlock(&opp_table_lock);
+
+	/*
+	 * Interconnect provider may use OPP too, hence icc_put() needs to be
+	 * invoked outside of the opp_table_lock in order to prevent nested
+	 * locking which happens when bandwidth of the ICC path is set to 0
+	 * by ICC core on release of the path.
+	 */
+	if (opp_table->paths) {
+		for (i = 0; i < opp_table->path_count; i++)
+			icc_put(opp_table->paths[i]);
+		kfree(opp_table->paths);
+	}
+
+	kfree(opp_table);
 }
 
 void dev_pm_opp_put_opp_table(struct opp_table *opp_table)
-- 
2.27.0