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

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Date: Fri, 15 Dec 2023 17:51:37 +0000
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Andy Shevchenko <andy.shevchenko@...il.com>
CC: "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>, George
 Stark <gnstark@...utedevices.com>, "kernel@...utedevices.com"
	<kernel@...utedevices.com>, "linuxppc-dev@...ts.ozlabs.org"
	<linuxppc-dev@...ts.ozlabs.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-leds@...r.kernel.org"
	<linux-leds@...r.kernel.org>
Subject: Re: [PATCH RFC v4-bis] locking: introduce devm_mutex_init



Le 15/12/2023 à 16:58, Andy Shevchenko a écrit :
> 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)?

Isn't needed, handled by Kconfig:

config DEBUG_MUTEXES
	bool "Mutex debugging: basic checks"
	depends on DEBUG_KERNEL && !PREEMPT_RT

> 
>> +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
>