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Message-ID: <550a22b0-dfc9-427f-bbf0-3c6854e9867d@redhat.com>
Date: Fri, 15 Dec 2023 20:30:51 -0500
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Subject: Re: [PATCH RFC v4-bis] locking: introduce devm_mutex_init
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To: Andy Shevchenko <andy.shevchenko@gmail.com>,
 Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: pavel@ucw.cz, lee@kernel.org, vadimp@nvidia.com, mpe@ellerman.id.au,
 npiggin@gmail.com, hdegoede@redhat.com, mazziesaccount@gmail.com,
 peterz@infradead.org, mingo@redhat.com, will@kernel.org,
 boqun.feng@gmail.com, nikitos.tr@gmail.com,
 George Stark <gnstark@salutedevices.com>, kernel@salutedevices.com,
 linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
 linux-leds@vger.kernel.org
References: <20231214173614.2820929-3-gnstark@salutedevices.com>
 <c16599b23afa853a44d13b906af5683027959a26.1702621174.git.christophe.leroy@csgroup.eu>
 <CAHp75VfBcmTBXXtU6o1x0Ea24wG-_Qb46opkS0EXKQ1Ynh0Mcw@mail.gmail.com>
From: Waiman Long <longman@redhat.com>
In-Reply-To: <CAHp75VfBcmTBXXtU6o1x0Ea24wG-_Qb46opkS0EXKQ1Ynh0Mcw@mail.gmail.com>
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On 12/15/23 10:58, Andy Shevchenko wrote:
> On Fri, Dec 15, 2023 at 8:23 AM Christophe Leroy
> <christophe.leroy@csgroup.eu> wrote:
>> From: George Stark <gnstark@salutedevices.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