linux-kernel - [PATCH v6 3/3] locking/mutex: Mark devm_mutex_init() as __must

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Message-Id: <20250609-must_check-devm_mutex_init-v6-3-9540d5df9704@weissschuh.net>
Date: Mon, 09 Jun 2025 22:38:39 +0200
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
 Waiman Long <longman@...hat.com>, Boqun Feng <boqun.feng@...il.com>, 
 Vicentiu Galanopulo <vicentiu.galanopulo@...ote-tech.co.uk>, 
 Will Deacon <will@...nel.org>, Han Xu <han.xu@....com>, 
 Haibo Chen <haibo.chen@....com>, Yogesh Gaur <yogeshgaur.83@...il.com>, 
 Mark Brown <broonie@...nel.org>, Lee Jones <lee@...nel.org>, 
 Pavel Machek <pavel@...nel.org>, Andrew Davis <afd@...com>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, 
 linux-kernel@...r.kernel.org, Bartosz Golaszewski <brgl@...ev.pl>, 
 Bartosz Golaszewski <bartosz.golaszewski@...aro.org>, 
 linux-spi@...r.kernel.org, imx@...ts.linux.dev, linux-leds@...r.kernel.org, 
 Thomas Weißschuh <linux@...ssschuh.net>
Subject: [PATCH v6 3/3] locking/mutex: Mark devm_mutex_init() as
 __must_check

Even if it's not critical, the avoidance of checking the error code
from devm_mutex_init() call today diminishes the point of using the devm
variant of it. Tomorrow it may even leak something. Enforce all callers
checking the return value through the compiler.

As devm_mutex_init() itself is a macro, it can not be annotated
directly. Annotate __devm_mutex_init() instead.
Unfortunately __must_check/warn_unused_result don't propagate through
statement expression. So move the statement expression into the argument
list of the call to __devm_mutex_init() through a helper macro.

Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
---
 include/linux/mutex.h | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index a039fa8c17807c700d3b61193feac0418cad1243..00afd341d293ddfcc0a427b576efdce044955e38 100644
--- a/include/linux/mutex.h
+++ b/include/linux/mutex.h
@@ -126,11 +126,11 @@ do {							\
 
 #ifdef CONFIG_DEBUG_MUTEXES
 
-int __devm_mutex_init(struct device *dev, struct mutex *lock);
+int __must_check __devm_mutex_init(struct device *dev, struct mutex *lock);
 
 #else
 
-static inline int __devm_mutex_init(struct device *dev, struct mutex *lock)
+static inline int __must_check __devm_mutex_init(struct device *dev, struct mutex *lock)
 {
 	/*
 	 * When CONFIG_DEBUG_MUTEXES is off mutex_destroy() is just a nop so
@@ -141,14 +141,17 @@ static inline int __devm_mutex_init(struct device *dev, struct mutex *lock)
 
 #endif
 
-#define devm_mutex_init(dev, mutex)			\
+#define __mutex_init_ret(mutex)				\
 ({							\
 	typeof(mutex) mutex_ = (mutex);			\
 							\
 	mutex_init(mutex_);				\
-	__devm_mutex_init(dev, mutex_);			\
+	mutex_;						\
 })
 
+#define devm_mutex_init(dev, mutex) \
+	__devm_mutex_init(dev, __mutex_init_ret(mutex))
+
 /*
  * See kernel/locking/mutex.c for detailed documentation of these APIs.
  * Also see Documentation/locking/mutex-design.rst.

-- 
2.49.0