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

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Message-ID: <550a22b0-dfc9-427f-bbf0-3c6854e9867d@redhat.com>
Date: Fri, 15 Dec 2023 20:30:51 -0500
From: Waiman Long <longman@...hat.com>
To: Andy Shevchenko <andy.shevchenko@...il.com>,
 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,
 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 12/15/23 10:58, Andy Shevchenko wrote:
> 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)?

CONFIG_DEBUG_MUTEXES and CONFIG_PREEMPT_RT are mutually exclusive. At 
most one of them can be set.

Cheers,
Longman