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@kernkonzept.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Tested-by: Stephan Gerhold <stephan.gerhold@kernkonzept.com>

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);