Le 06/12/2023 à 19:58, George Stark a écrit : > [Vous ne recevez pas souvent de courriers de gnstark@xxxxxxxxxxxxxxxxx. > Découvrez pourquoi ceci est important à > https://aka.ms/LearnAboutSenderIdentification ] > > Hello Hans > > Thanks for the review. > > On 12/6/23 18:01, Hans de Goede wrote: >> Hi George, >> >> On 12/4/23 19:05, George Stark wrote: >>> 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 <gnstark@xxxxxxxxxxxxxxxxx> >>> --- >>> 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. > > Honestly saying I don't like unnecessary devres allocation either but > the proposed approach has its own price: > > 1) we'll have more than one place with branching if mutex_destroy is > empty or not using indirect condition. If suddenly mutex_destroy is > extended for non-debug code (in upstream branch or e.g. by someone for > local debug) than there'll be a problem. > > 2) If mutex_destroy is empty or not depends on CONFIG_PREEMPT_RT option > too. When CONFIG_PREEMPT_RT is on mutex_destroy is always empty. > > As I see it only the mutex interface (mutex.h) has to say definitely if > mutex_destroy must be called. Probably we could add some define to > include/linux/mutex.h,like IS_MUTEX_DESTROY_REQUIRED and declare it near > mutex_destroy definition itself. > > I tried to put devm_mutex_init itself in mutex.h and it could've helped > too but it's not the place for devm API. > What do you mean by "it's not the place for devm API" ? If you do a 'grep devm_ include/linux/' you'll find devm_ functions in almost 100 .h files. Why wouldn't mutex.h be the place for devm_mutex_init() ? Christophe
