linux-kernel - [PATCH 3/6] regulator: core: simplify nested locking

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Message-Id: <7d678e7b55e88e630491086f59120253fabeb386.1692484240.git.mirq-linux@rere.qmqm.pl>
Date:   Sun, 20 Aug 2023 00:46:09 +0200
From:   Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:     Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>
Cc:     Dmitry Osipenko <digetx@...il.com>, linux-kernel@...r.kernel.org,
        Douglas Anderson <dianders@...omium.org>
Subject: [PATCH 3/6] regulator: core: simplify nested locking

Simplify regulator locking by removing locking around locking.
rdev->ref check when unlocking is moved inside the critical section.

This patch depends on 12235da8c80a ("kernel/locking: Add context to
ww_mutex_trylock()").

Signed-off-by: Michał Mirosław <mirq-linux@...e.qmqm.pl>
---
 drivers/regulator/core.c | 19 +++++--------------
 1 file changed, 5 insertions(+), 14 deletions(-)

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index 921c7039baa3..87e54b776a0f 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -34,7 +34,6 @@
 #include "internal.h"
 
 static DEFINE_WW_CLASS(regulator_ww_class);
-static DEFINE_MUTEX(regulator_nesting_mutex);
 static DEFINE_MUTEX(regulator_list_mutex);
 static LIST_HEAD(regulator_map_list);
 static LIST_HEAD(regulator_ena_gpio_list);
@@ -143,23 +142,18 @@ static inline int regulator_lock_nested(struct regulator_dev *rdev,
 {
 	int ret = 0;
 
-	mutex_lock(&regulator_nesting_mutex);
-
 	if (!ww_mutex_trylock(&rdev->mutex, ww_ctx) &&
-	    rdev->mutex_owner != current) {
-		mutex_unlock(&regulator_nesting_mutex);
+	    READ_ONCE(rdev->mutex_owner) != current) {
 		ret = ww_mutex_lock(&rdev->mutex, ww_ctx);
+
 		if (ret == -EDEADLK)
 			return ret;
-		mutex_lock(&regulator_nesting_mutex);
 	}
 
 	rdev->ref_cnt++;
 	rdev->mutex_owner = current;
 
-	mutex_unlock(&regulator_nesting_mutex);
-
-	return ret;
+	return 0;
 }
 
 /**
@@ -186,16 +180,13 @@ static void regulator_lock(struct regulator_dev *rdev)
  */
 static void regulator_unlock(struct regulator_dev *rdev)
 {
-	mutex_lock(&regulator_nesting_mutex);
+	if (WARN_ON_ONCE(rdev->ref_cnt <= 0))
+		return;
 
 	if (--rdev->ref_cnt == 0) {
 		rdev->mutex_owner = NULL;
 		ww_mutex_unlock(&rdev->mutex);
 	}
-
-	WARN_ON_ONCE(rdev->ref_cnt < 0);
-
-	mutex_unlock(&regulator_nesting_mutex);
 }
 
 /**
-- 
2.39.2