linux-kernel - Re: [PATCH v2 01/10] devm-helpers: introduce devm_mutex

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Message-ID: <57ea099a-8b88-4b16-9b54-b81e5b28bcb6@salutedevices.com>
Date:   Thu, 7 Dec 2023 15:51:44 +0300
From:   George Stark <gnstark@...utedevices.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Andy Shevchenko <andy.shevchenko@...il.com>
CC:     Hans de Goede <hdegoede@...hat.com>, "pavel@....cz" <pavel@....cz>,
        "lee@...nel.org" <lee@...nel.org>,
        "vadimp@...dia.com" <vadimp@...dia.com>,
        "mpe@...erman.id.au" <mpe@...erman.id.au>,
        "npiggin@...il.com" <npiggin@...il.com>,
        "mazziesaccount@...il.com" <mazziesaccount@...il.com>,
        "jic23@...nel.org" <jic23@...nel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        Waiman Long <longman@...hat.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "will@...nel.org" <will@...nel.org>,
        "boqun.feng@...il.com" <boqun.feng@...il.com>,
        "linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "kernel@...utedevices.com" <kernel@...utedevices.com>
Subject: Re: [PATCH v2 01/10] devm-helpers: introduce devm_mutex_init



On 12/7/23 15:28, Christophe Leroy wrote:
> 
> 
> Le 07/12/2023 à 13:02, Andy Shevchenko a écrit :
>> On Thu, Dec 7, 2023 at 1:23 AM George Stark <gnstark@...utedevices.com> wrote:
>>> On 12/7/23 01:37, Christophe Leroy wrote:
>>>> Le 06/12/2023 à 23:14, Christophe Leroy a écrit :
>>
>> ...
>>
>>>> Looking at it closer, I have the feeling that you want to do similar to
>>>> devm_gpio_request() in linux/gpio.h :
>>>>
>>>> In linux/mutex.h, add a prototype for devm_mutex_init() when
>>>> CONFIG_DEBUG_MUTEXES is defined and an empty static inline otherwise.
>>>> Then define devm_mutex_init() in kernel/locking/mutex-debug.c
>>>
>>> Yes, this would be almost perfect decision. BTW just as in linux/gpio.h
>>> we wouldn't have to include whole "linux/device.h" into mutex.h, only
>>> add forward declaration of struct device;
>>
>> In case you place it into a C-file. Otherwise you need a header for
>> the API and that is not acceptable for mutex.h.
>>
> 
> Right, that's the reason why I'm suggesting to define devm_mutex_init()
> in kernel/locking/mutex-debug.c.
> 
> In linux/mutex.h, you define a stub for when CONFIG_DEBUG_MUTEXES is not
> set, and the prototype of devm_mutex_init() when CONFIG_DEBUG_MUTEXES is
> set.

Something like this:

diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index a33aa9eb9fc3..4a6041a7fd44 100644
--- a/include/linux/mutex.h
+++ b/include/linux/mutex.h
@@ -21,6 +21,8 @@
  #include <linux/debug_locks.h>
  #include <linux/cleanup.h>

+struct device;
+
  #ifdef CONFIG_DEBUG_LOCK_ALLOC
  # define __DEP_MAP_MUTEX_INITIALIZER(lockname)			\
  		, .dep_map = {					\
@@ -127,6 +129,20 @@ extern void __mutex_init(struct mutex *lock, const 
char *name,
   */
  extern bool mutex_is_locked(struct mutex *lock);

+#ifdef CONFIG_DEBUG_MUTEXES
+
+extern int devm_mutex_init(struct device *dev, struct mutex *lock);
+
+#else
+
+static inline int devm_mutex_init(struct device *dev, struct mutex *lock)
+{
+	mutex_init(lock);
+	return 0;
+}
+
+#endif
+
  #else /* !CONFIG_PREEMPT_RT */
  /*
   * Preempt-RT variant based on rtmutexes.
@@ -169,6 +185,13 @@ do {							\
  							\
  	__mutex_init((mutex), #mutex, &__key);		\
  } while (0)
+
+static inline int devm_mutex_init(struct device *dev, struct mutex *lock)
+{
+	mutex_init(lock);
+	return 0;
+}
+
  #endif /* CONFIG_PREEMPT_RT */

  /*
diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c
index bc8abb8549d2..d50dfa06e82c 100644
--- a/kernel/locking/mutex-debug.c
+++ b/kernel/locking/mutex-debug.c
@@ -19,6 +19,7 @@
  #include <linux/kallsyms.h>
  #include <linux/interrupt.h>
  #include <linux/debug_locks.h>
+#include <linux/device.h>

  #include "mutex.h"

@@ -104,3 +105,25 @@ void mutex_destroy(struct mutex *lock)
  }

  EXPORT_SYMBOL_GPL(mutex_destroy);
+
+static void devm_mutex_release(void *res)
+{
+	mutex_destroy(res);
+}
+
+/**
+ * devm_mutex_init - Resource-managed mutex initialization
+ * @dev:	Device which lifetime mutex is bound to
+ * @lock:	Pointer to a mutex
+ *
+ * Initialize mutex which is automatically destroyed when the driver is 
detached.
+ *
+ * Returns: 0 on success or a negative error code on failure.
+ */
+int devm_mutex_init(struct device *dev, struct mutex *lock)
+{
+	mutex_init(lock);
+	return devm_add_action_or_reset(dev, devm_mutex_release, lock);
+}
+
+EXPORT_SYMBOL_GPL(devm_mutex_init);
\ No newline at end of file


-- 
Best regards
George