Re: [PATCH v2 01/10] devm-helpers: introduce devm_mutex_init
From: Hans de Goede <hidden>
Date: 2023-12-06 15:01:11
Also in:
linux-leds, lkml
Hi George, On 12/4/23 19:05, George Stark wrote:
quoted hunk ↗ jump to hunk
Using of devm API leads to 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() is extended so introduce devm_mutex_init(). Signed-off-by: George Stark <redacted> --- include/linux/devm-helpers.h | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+)diff --git a/include/linux/devm-helpers.h b/include/linux/devm-helpers.h index 74891802200d..2f56e476776f 100644 --- a/include/linux/devm-helpers.h +++ b/include/linux/devm-helpers.h@@ -76,4 +76,22 @@ static inline int devm_work_autocancel(struct device *dev, return devm_add_action(dev, devm_work_drop, w); } +static inline void devm_mutex_release(void *res) +{ + mutex_destroy(res); +} + +/** + * devm_mutex_init - Resource-managed mutex initialization + * @dev: Device which lifetime work is bound to + * @lock: Pointer to a mutex + * + * Initialize mutex which is automatically destroyed when driver is detached. + */ +static inline int devm_mutex_init(struct device *dev, struct mutex *lock) +{ + mutex_init(lock); + return devm_add_action_or_reset(dev, devm_mutex_release, lock); +} + #endif
mutex_destroy() only actually does anything if CONFIG_DEBUG_MUTEXES
is set, otherwise it is an empty inline-stub.
Adding a devres resource to the device just to call an empty inline
stub which is a no-op seems like a waste of resources. IMHO it
would be better to change this to:
static inline int devm_mutex_init(struct device *dev, struct mutex *lock)
{
mutex_init(lock);
#ifdef CONFIG_DEBUG_MUTEXES
return devm_add_action_or_reset(dev, devm_mutex_release, lock);
#else
return 0;
#endif
}
To avoid the unnecessary devres allocation when
CONFIG_DEBUG_MUTEXES is not set.
Regards,
Hans