linux-kernel - Re: [PATCH v6 1/9] locking/mutex: introduce devm_mutex

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Message-ID: <9fe2eaef-0407-4a96-b603-e7f6579110b6@redhat.com>
Date: Thu, 14 Mar 2024 09:32:48 -0400
From: Waiman Long <longman@...hat.com>
To: George Stark <gnstark@...utedevices.com>, andy.shevchenko@...il.com,
 pavel@....cz, lee@...nel.org, vadimp@...dia.com, mpe@...erman.id.au,
 npiggin@...il.com, christophe.leroy@...roup.eu, hdegoede@...hat.com,
 mazziesaccount@...il.com, peterz@...radead.org, mingo@...hat.com,
 will@...nel.org, boqun.feng@...il.com, nikitos.tr@...il.com,
 marek.behun@....cz, kabel@...nel.org
Cc: linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org,
 linuxppc-dev@...ts.ozlabs.org, kernel@...utedevices.com
Subject: Re: [PATCH v6 1/9] locking/mutex: introduce devm_mutex_init


On 3/14/24 04:45, George Stark wrote:
> Using of devm API leads to a certain order of releasing resources.
> So all dependent resources which are not devm-wrapped should be deleted
> with respect to devm-release order. Mutex is one of such objects that
> often is bound to other resources and has no own devm wrapping.
> Since mutex_destroy() actually does nothing in non-debug builds
> frequently calling mutex_destroy() is just ignored which is safe for now
> but wrong formally and can lead to a problem if mutex_destroy() will be
> extended so introduce devm_mutex_init()
>
> Signed-off-by: George Stark <gnstark@...utedevices.com>
> Suggested by-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>   include/linux/mutex.h        | 27 +++++++++++++++++++++++++++
>   kernel/locking/mutex-debug.c | 11 +++++++++++
>   2 files changed, 38 insertions(+)
>
> diff --git a/include/linux/mutex.h b/include/linux/mutex.h
> index 67edc4ca2bee..f57e005ded24 100644
> --- a/include/linux/mutex.h
> +++ b/include/linux/mutex.h
> @@ -22,6 +22,8 @@
>   #include <linux/cleanup.h>
>   #include <linux/mutex_types.h>
>   
> +struct device;
> +
>   #ifdef CONFIG_DEBUG_LOCK_ALLOC
>   # define __DEP_MAP_MUTEX_INITIALIZER(lockname)			\
>   		, .dep_map = {					\
> @@ -117,6 +119,31 @@ do {							\
>   } while (0)
>   #endif /* CONFIG_PREEMPT_RT */
>   
> +#ifdef CONFIG_DEBUG_MUTEXES
> +
> +int __devm_mutex_init(struct device *dev, struct mutex *lock);
> +
> +#else
> +
> +static inline int __devm_mutex_init(struct device *dev, struct mutex *lock)
> +{
> +	/*
> +	 * When CONFIG_DEBUG_MUTEXES is off mutex_destroy is just a nop so
> +	 * no really need to register it in devm subsystem.
> +	 */
> +	return 0;
> +}
> +
> +#endif
> +
> +#define devm_mutex_init(dev, mutex)			\
> +({							\
> +	typeof(mutex) mutex_ = (mutex);			\
> +							\
> +	mutex_init(mutex_);				\
> +	__devm_mutex_init(dev, mutex_);			\
> +})
> +
>   /*
>    * See kernel/locking/mutex.c for detailed documentation of these APIs.
>    * Also see Documentation/locking/mutex-design.rst.
> diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c
> index bc8abb8549d2..6aa77e3dc82e 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"
>   
> @@ -89,6 +90,16 @@ void debug_mutex_init(struct mutex *lock, const char *name,
>   	lock->magic = lock;
>   }
>   
> +static void devm_mutex_release(void *res)
> +{
> +	mutex_destroy(res);
> +}
> +
> +int __devm_mutex_init(struct device *dev, struct mutex *lock)
> +{
> +	return devm_add_action_or_reset(dev, devm_mutex_release, lock);
> +}
> +
>   /***
>    * mutex_destroy - mark a mutex unusable
>    * @lock: the mutex to be destroyed
Acked-by: Waiman Long <longman@...hat.com>