linux-kernel - Re: [PATCH RFC v4-bis] locking: introduce devm_mutex

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Message-ID: <CAHp75VfBcmTBXXtU6o1x0Ea24wG-_Qb46opkS0EXKQ1Ynh0Mcw@mail.gmail.com>
Date: Fri, 15 Dec 2023 17:58:44 +0200
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: pavel@....cz, lee@...nel.org, vadimp@...dia.com, mpe@...erman.id.au, 
	npiggin@...il.com, hdegoede@...hat.com, mazziesaccount@...il.com, 
	peterz@...radead.org, mingo@...hat.com, will@...nel.org, longman@...hat.com, 
	boqun.feng@...il.com, nikitos.tr@...il.com, 
	George Stark <gnstark@...utedevices.com>, kernel@...utedevices.com, 
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org, 
	linux-leds@...r.kernel.org
Subject: Re: [PATCH RFC v4-bis] locking: introduce devm_mutex_init

On Fri, Dec 15, 2023 at 8:23 AM Christophe Leroy
<christophe.leroy@...roup.eu> wrote:
>
> From: George Stark <gnstark@...utedevices.com>
>
> 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()

Missing period.

...

>  } while (0)
>  #endif /* CONFIG_PREEMPT_RT */

^^^ (1)

> +struct device;
> +
> +/*
> + * devm_mutex_init() registers a function that calls mutex_destroy()
> + * when the ressource is released.
> + *
> + * When mutex_destroy() is a not, there is no need to register that
> + * function.
> + */
> +#ifdef CONFIG_DEBUG_MUTEXES

Shouldn't this be

#if defined(CONFIG_DEBUG_MUTEXES) && !defined(CONFIG_PREEMPT_RT)

(see (1) as well)?

> +void mutex_destroy(struct mutex *lock);
> +int devm_mutex_init(struct device *dev, struct mutex *lock);
> +#else
> +static inline void mutex_destroy(struct mutex *lock) {}
> +
> +static inline int devm_mutex_init(struct device *dev, struct mutex *lock)
> +{
> +       mutex_init(lock);
> +       return 0;
> +}
> +#endif

-- 
With Best Regards,
Andy Shevchenko