On 3/7/24 04:56, Marek Behún wrote:
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
Making devm_mutex_init() a function will make all the devm_mutex share the same lockdep key. Making it a macro will make each caller of devm_mutex_init() have a distinct lockdep key. It all depends on whether all the devm_mutexes have the same lock usage pattern or not and whether it is possible for one devm_mutex to be nested inside another. So either way can be fine depending on the mutex usage pattern. My suggestion is to use a function, if possible, unless it will cause a false positive lockdep splat as there is a limit on the maximum # of lockdep keys that can be used.
Cheers, Longman
