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

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Message-ID: <08cf2729-78c4-44a3-ac3f-78c652a527ff@csgroup.eu>
Date:   Thu, 7 Dec 2023 13:01:59 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     George Stark <gnstark@...utedevices.com>,
        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



Le 07/12/2023 à 13:51, George Stark a écrit :
> 
> 
> 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

There is already a CONFIG_DEBUG_MUTEXES block, can you re-use it ?

> +
> +extern int devm_mutex_init(struct device *dev, struct mutex *lock);

'extern' is pointless and deprecated for function prototypes.
I know the kernel is full of them, but it is not a good reason to add 
new ones.

> +
> +#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
> 
>