linux-kernel - Re: [PATCH v5 02/10] locking/mutex: introduce devm_mutex

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Message-ID: <479472f8-58a1-47af-9f83-c75f89f67b00@csgroup.eu>
Date: Tue, 12 Mar 2024 05:44:17 +0000
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Waiman Long <longman@...hat.com>, George Stark
	<gnstark@...utedevices.com>, Marek Behún
	<marek.behun@....cz>
CC: "andy.shevchenko@...il.com" <andy.shevchenko@...il.com>, "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>,
	"boqun.feng@...il.com" <boqun.feng@...il.com>, "nikitos.tr@...il.com"
	<nikitos.tr@...il.com>, "kabel@...nel.org" <kabel@...nel.org>,
	"linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"kernel@...utedevices.com" <kernel@...utedevices.com>
Subject: Re: [PATCH v5 02/10] locking/mutex: introduce devm_mutex_init



Le 12/03/2024 à 02:10, Waiman Long a écrit :
> On 3/11/24 19:47, George Stark wrote:
>> Hello Waiman, Marek
>>
>> Thanks for the review.
>>
>> I've never used lockdep for debug but it seems preferable to
>> keep that feature working. It could be look like this:
>>
>> diff --git a/include/linux/mutex.h b/include/linux/mutex.h
>> index f7611c092db7..574f6de6084d 100644
>> --- a/include/linux/mutex.h
>> +++ b/include/linux/mutex.h
>> @@ -22,6 +22,8 @@
>>  #include <linux/cleanup.h>
>>  #include <linux/mutex_types.h>
>>
>> +struct device;
>> +
>>  #ifdef CONFIG_DEBUG_LOCK_ALLOC
>>  # define __DEP_MAP_MUTEX_INITIALIZER(lockname)            \
>>          , .dep_map = {                    \
>> @@ -115,10 +117,31 @@ do {                            \
>>
>>  #ifdef CONFIG_DEBUG_MUTEXES
>>
>> +int debug_devm_mutex_init(struct device *dev, struct mutex *lock);
>> +
>> +#define devm_mutex_init(dev, mutex)            \
>> +({                            \
>> +    int ret;                    \
>> +    mutex_init(mutex);                \
>> +    ret = debug_devm_mutex_init(dev, mutex);    \
>> +    ret;                        \
>> +})
> 
> The int ret variable is not needed. The macro can just end with 
> debug_devm_mutex_init().
> 
> 
>> +
>>  void mutex_destroy(struct mutex *lock);
>>
>>  #else
>>
>> +/*
>> +* When CONFIG_DEBUG_MUTEXES is off mutex_destroy is just a nop so
>> +* there's no really need to register it in devm subsystem.
> "no really need"?
>> +*/
>> +#define devm_mutex_init(dev, mutex)            \
>> +({                            \
>> +    typecheck(struct device *, dev);        \
>> +    mutex_init(mutex);                \
>> +    0;                        \
>> +})
> 
> Do we need a typecheck() here? Compilation will fail with 
> CONFIG_DEBUG_MUTEXES if dev is not a device pointer.

I guess the idea is to have it fail _also_ when CONFIG_DEBUG_MUTEXES is 
not selected, in order to discover errors as soon as possible.

> 
> 
>> +
>>  static inline void mutex_destroy(struct mutex *lock) {}
>>
>>  #endif
>> diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c
>> index bc8abb8549d2..967a5367c79a 100644
>> --- a/kernel/locking/mutex-debug.c
>> +++ b/kernel/locking/mutex-debug.c
>> @@ -19,6 +19,7 @@
>>  #include <linux/kallsyms.h>
>>  #include <linux/interrupt.h>
>>  #include <linux/debug_locks.h>
>> +#include <linux/device.h>
>>
>>  #include "mutex.h"
>>
>> @@ -89,6 +90,16 @@ void debug_mutex_init(struct mutex *lock, const 
>> char *name,
>>      lock->magic = lock;
>>  }
>>
>> +static void devm_mutex_release(void *res)
>> +{
>> +    mutex_destroy(res);
>> +}
>> +
>> +int debug_devm_mutex_init(struct device *dev, struct mutex *lock)
>> +{
>> +    return devm_add_action_or_reset(dev, devm_mutex_release, lock);
>> +}
>> +
>>  /***
>>   * mutex_destroy - mark a mutex unusable
>>   * @lock: the mutex to be destroyed
>