linux-kernel - [PATCH 2/2] OPP: Protect `lazy_opp_tables` list with `opp_table

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Message-Id: <c0bac65236cf77fa8ac17c2645449544b73a0104.1686210112.git.viresh.kumar@linaro.org>
Date:   Thu,  8 Jun 2023 13:13:23 +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 J. Wysocki" <rafael@...nel.org>,
        Stephan Gerhold <stephan.gerhold@...nkonzept.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] OPP: Protect `lazy_opp_tables` list with `opp_table_lock`

The `opp_table_lock` lock is already used to protect the list elsewhere,
use it while adding or removing entries from it.

Reported-by: Stephan Gerhold <stephan.gerhold@...nkonzept.com>
Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
---
Stephan: Can you please give this a try ?

 drivers/opp/of.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/opp/of.c b/drivers/opp/of.c
index c740a907ef76..ac2179d5da4c 100644
--- a/drivers/opp/of.c
+++ b/drivers/opp/of.c
@@ -21,7 +21,7 @@
 
 #include "opp.h"
 
-/* OPP tables with uninitialized required OPPs */
+/* OPP tables with uninitialized required OPPs, protected by opp_table_lock */
 static LIST_HEAD(lazy_opp_tables);
 
 /*
@@ -148,7 +148,10 @@ static void _opp_table_free_required_tables(struct opp_table *opp_table)
 
 	opp_table->required_opp_count = 0;
 	opp_table->required_opp_tables = NULL;
+
+	mutex_lock(&opp_table_lock);
 	list_del(&opp_table->lazy);
+	mutex_unlock(&opp_table_lock);
 }
 
 /*
@@ -197,8 +200,15 @@ static void _opp_table_alloc_required_tables(struct opp_table *opp_table,
 	}
 
 	/* Let's do the linking later on */
-	if (lazy)
+	if (lazy) {
+		/*
+		 * The OPP table is not held while allocating the table, take it
+		 * now to avoid corruption to the lazy_opp_tables list.
+		 */
+		mutex_lock(&opp_table_lock);
 		list_add(&opp_table->lazy, &lazy_opp_tables);
+		mutex_unlock(&opp_table_lock);
+	}
 	else
 		_update_set_required_opps(opp_table);
 
-- 
2.31.1.272.g89b43f80a514