linux-kernel - Re: [PATCH v5 02/10] locking/mutex: introduce devm_mutex

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Date: Thu, 7 Mar 2024 13:50:54 +0000
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: George Stark <gnstark@...utedevices.com>, "andy.shevchenko@...il.com"
	<andy.shevchenko@...il.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>, "hdegoede@...hat.com" <hdegoede@...hat.com>,
	"mazziesaccount@...il.com" <mazziesaccount@...il.com>, "peterz@...radead.org"
	<peterz@...radead.org>, "mingo@...hat.com" <mingo@...hat.com>,
	"will@...nel.org" <will@...nel.org>, "longman@...hat.com"
	<longman@...hat.com>, "boqun.feng@...il.com" <boqun.feng@...il.com>,
	"nikitos.tr@...il.com" <nikitos.tr@...il.com>, "kabel@...nel.org"
	<kabel@...nel.org>
CC: "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 v5 02/10] locking/mutex: introduce devm_mutex_init



Le 07/03/2024 à 03:40, George Stark a écrit :
> [Vous ne recevez pas souvent de courriers de gnstark@...utedevices.com. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
> 
> 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>
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>   Hello Christophe. Hope you don't mind I put you SoB tag because you helped alot
>   to make this patch happen.

Up to you, I sent a RFC patch based on yours with my ideas included 
because an exemple is easier than a lot of words for understanding, and 
my scripts automatically sets the Signed-off-by: but feel free to change 
it to Suggested-by:

Christophe

> 
>   include/linux/mutex.h        | 13 +++++++++++++
>   kernel/locking/mutex-debug.c | 22 ++++++++++++++++++++++
>   2 files changed, 35 insertions(+)
> 
> diff --git a/include/linux/mutex.h b/include/linux/mutex.h
> index f7611c092db7..9bcf72cb941a 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 = {                                  \
> @@ -115,10 +117,21 @@ do {                                                      \
> 
>   #ifdef CONFIG_DEBUG_MUTEXES
> 
> +int devm_mutex_init(struct device *dev, struct mutex *lock);
>   void mutex_destroy(struct mutex *lock);
> 
>   #else
> 
> +static inline int devm_mutex_init(struct device *dev, struct mutex *lock)
> +{
> +       /*
> +        * since mutex_destroy is nop actually there's no need to register it
> +        * in devm subsystem.
> +        */
> +       mutex_init(lock);
> +       return 0;
> +}
> +
>   static inline void mutex_destroy(struct mutex *lock) {}
> 
>   #endif
> diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c
> index bc8abb8549d2..c9efab1a8026 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 +105,24 @@ 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);
> --
> 2.25.1
>