On Thu, Mar 07, 2024 at 05:40:26AM +0300, 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@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
> ---
> Hello Christophe. Hope you don't mind I put you SoB tag because you helped alot
> to make this patch happen.
>
> include/linux/mutex.h | 13 +++++++++++++
> kernel/locking/mutex-debug.c | 22 ++++++++++++++++++++++
> 2 files changed, 35 insertions(+)
>
> diff --git a/include/linux/mutex.h b/include/linux/mutex.h
> index f7611c092db7..9bcf72cb941a 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 +117,21 @@ do { \
>
> #ifdef CONFIG_DEBUG_MUTEXES
>
> +int devm_mutex_init(struct device *dev, struct mutex *lock);
> void mutex_destroy(struct mutex *lock);
>
> #else
>
> +static inline int devm_mutex_init(struct device *dev, struct mutex *lock)
> +{
> + /*
> + * since mutex_destroy is nop actually there's no need to register it
> + * in devm subsystem.
> + */
> + mutex_init(lock);
> + return 0;
> +}
> +
> 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..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);
Hi George,
look at
https://lore.kernel.org/lkml/7013bf9e-2663-4613-ae61-61872e81355b@xxxxxxxxxx/
where Matthew and Hans explain that devm_mutex_init needs to be a macro
because of the static lockdep key.
so this should be something like:
static inline int __devm_mutex_init(struct device *dev, struct mutex *mutex,
const char *name,
struct lock_class_key *key)
{
__mutex_init(mutex, name, key);
return devm_add_action_or_reset(dev, devm_mutex_release, mutex);
}
#define devm_mutex_init(dev, mutex) \
do { \
static struct lock_class_key __key; \
\
__devm_mutex_init(dev, (mutex), #mutex, &__key); \
} while (0);
Marek
