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Message-ID: <27479d7f-fe9a-4ae7-8490-2f070fa7a16d@csgroup.eu>
Date: Thu, 14 Dec 2023 19:47:20 +0000
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: 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>, "longman@...hat.com"
<longman@...hat.com>, "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 18:36, George Stark a écrit :
> [Vous ne recevez pas souvent de courriers de gnstark@...utedevices.com. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
>
> 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);
> +
> +#else
> +
> +static inline int devm_mutex_init(struct device *dev, struct mutex *lock)
> +{
> + mutex_init(lock);
> + return 0;
> +}
> +
> +#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);
> --
> 2.25.1
>
I think it would make sense to keep mutex_destroy() and
devm_mutex_init() together, see exemple below:
diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index ebd03ff1ef66..c620759ff85b 100644
--- a/include/linux/mutex.h
+++ b/include/linux/mutex.h
@@ -83,14 +83,10 @@ struct mutex {
#define __DEBUG_MUTEX_INITIALIZER(lockname) \
, .magic = &lockname
-extern void mutex_destroy(struct mutex *lock);
-
#else
# define __DEBUG_MUTEX_INITIALIZER(lockname)
-static inline void mutex_destroy(struct mutex *lock) {}
-
#endif
/**
@@ -131,10 +127,13 @@ extern bool mutex_is_locked(struct mutex *lock);
#ifdef CONFIG_DEBUG_MUTEXES
+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);
@@ -169,8 +168,6 @@ extern void __mutex_rt_init(struct mutex *lock,
const char *name,
struct lock_class_key *key);
extern int mutex_trylock(struct mutex *lock);
-static inline void mutex_destroy(struct mutex *lock) { }
-
#define mutex_is_locked(l) rt_mutex_base_is_locked(&(l)->rtmutex)
#define __mutex_init(mutex, name, key) \
@@ -186,6 +183,8 @@ do { \
__mutex_init((mutex), #mutex, &__key); \
} while (0)
+static inline void mutex_destroy(struct mutex *lock) { }
+
static inline int devm_mutex_init(struct device *dev, struct mutex *lock)
{
mutex_init(lock);
---
Would also be nice to have a comment explaining that when
mutex_destroy() is a nop, devm_mutext_init() doesn't need to register a
release function.
Either way,
Reviewed-by: christophe.leroy@...roup.eu
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