Re: [PATCH RFC v4-bis] locking: introduce devm_mutex_init

[Christophe Leroy]

Le 15/12/2023 à 16:58, Andy Shevchenko a écrit :
> On Fri, Dec 15, 2023 at 8:23 AM Christophe Leroy
> <christophe.leroy@xxxxxxxxxx> wrote:
>>
>> From: George Stark <gnstark@xxxxxxxxxxxxxxxxx>
>>
>> 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
>