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Message-ID: <b158ca2b-7300-4ad0-82b8-e1442d267734@csgroup.eu>
Date: Thu, 14 Dec 2023 19:53:33 +0000
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Waiman Long <longman@...hat.com>, George Stark
<gnstark@...utedevices.com>, "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>
CC: "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 v4 02/10] locking: introduce devm_mutex_init
Le 14/12/2023 à 19:48, Waiman Long a écrit :
>
> On 12/14/23 12:36, George Stark wrote:
>> 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()
>>
>> Signed-off-by: George Stark <gnstark@...utedevices.com>
>> ---
>> include/linux/mutex.h | 23 +++++++++++++++++++++++
>> kernel/locking/mutex-debug.c | 22 ++++++++++++++++++++++
>> 2 files changed, 45 insertions(+)
>>
>> diff --git a/include/linux/mutex.h b/include/linux/mutex.h
>> index a33aa9eb9fc3..ebd03ff1ef66 100644
>> --- a/include/linux/mutex.h
>> +++ b/include/linux/mutex.h
>> @@ -21,6 +21,8 @@
>> #include <linux/debug_locks.h>
>> #include <linux/cleanup.h>
>> +struct device;
>> +
>> #ifdef CONFIG_DEBUG_LOCK_ALLOC
>> # define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
>> , .dep_map = { \
>> @@ -127,6 +129,20 @@ extern void __mutex_init(struct mutex *lock,
>> const char *name,
>> */
>> extern bool mutex_is_locked(struct mutex *lock);
>> +#ifdef CONFIG_DEBUG_MUTEXES
>> +
>> +int devm_mutex_init(struct device *dev, struct mutex *lock);
> Please add "extern" to the function declaration to be consistent with
> other functional declarations in mutex.h.
'extern' is pointless and deprecated on function prototypes. Already
having some is not a good reason to add new ones, errors from the past
should be avoided nowadays. With time they should all disappear so don't
add new ones.
>> +
>> +#else
>> +
>> +static inline int devm_mutex_init(struct device *dev, struct mutex
>> *lock)
>> +{
>> + mutex_init(lock);
>> + return 0;
>> +}
>
> I would prefer you to add a devm_mutex_init macro after the function
> declaration and put this inline function at the end of header if the
> devm_mutex_init macro isn't defined. In this way, you don't need to
> repeat this inline function twice as it has no dependency on PREEMPT_RT.
It is already done that way for other functions in that file. Should be
kept consistant. I agree with you it is not ideal, maybe we should
rework that file completely but I don't like the idea of a
devm_mutex_init macro for that.
Christophe
>
> By doing this, you can also move the function declaration right after
> mutex_destroy() without the need to add another #ifdef
> CONFIG_DEBUG_MUTEXES block.
>
>> +
>> +#endif
>> +
>> #else /* !CONFIG_PREEMPT_RT */
>> /*
>> * Preempt-RT variant based on rtmutexes.
>> @@ -169,6 +185,13 @@ do { \
>> \
>> __mutex_init((mutex), #mutex, &__key); \
>> } while (0)
>> +
>> +static inline int devm_mutex_init(struct device *dev, struct mutex
>> *lock)
>> +{
>> + mutex_init(lock);
>> + return 0;
>> +}
>> +
>> #endif /* CONFIG_PREEMPT_RT */
>> /*
>> diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c
>> index bc8abb8549d2..c9efab1a8026 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"
>> @@ -104,3 +105,24 @@ void mutex_destroy(struct mutex *lock)
>> }
>> EXPORT_SYMBOL_GPL(mutex_destroy);
>> +
>> +static void devm_mutex_release(void *res)
>> +{
>> + mutex_destroy(res);
>> +}
>> +
>> +/**
>> + * devm_mutex_init - Resource-managed mutex initialization
>> + * @dev: Device which lifetime mutex is bound to
>> + * @lock: Pointer to a mutex
>> + *
>> + * Initialize mutex which is automatically destroyed when the driver
>> is detached.
>> + *
>> + * Returns: 0 on success or a negative error code on failure.
>> + */
>> +int devm_mutex_init(struct device *dev, struct mutex *lock)
>> +{
>> + mutex_init(lock);
>> + return devm_add_action_or_reset(dev, devm_mutex_release, lock);
>> +}
>> +EXPORT_SYMBOL_GPL(devm_mutex_init);
>
> The mutex-debug.c change looks fine to me.
>
> Cheers,
> Longman
>
>
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