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 <[email protected]>
---
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
On 12/14/23 12:36, 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 <[email protected]>
> ---
> 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);
Please add "extern" to the function declaration to be consistent with
other functional declarations in mutex.h.
> +
> +#else
> +
> +static inline int devm_mutex_init(struct device *dev, struct mutex *lock)
> +{
> + mutex_init(lock);
> + return 0;
> +}
I would prefer you to add a devm_mutex_init macro after the function
declaration and put this inline function at the end of header if the
devm_mutex_init macro isn't defined. In this way, you don't need to
repeat this inline function twice as it has no dependency on PREEMPT_RT.
By doing this, you can also move the function declaration right after
mutex_destroy() without the need to add another #ifdef
CONFIG_DEBUG_MUTEXES block.
> +
> +#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);
The mutex-debug.c change looks fine to me.
Cheers,
Longman
Le 14/12/2023 à 18:36, George Stark a écrit :
> [Vous ne recevez pas souvent de courriers de [email protected]. 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 <[email protected]>
> ---
> 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: [email protected]
Le 14/12/2023 à 19:48, Waiman Long a écrit :
>
> On 12/14/23 12:36, 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 <[email protected]>
>> ---
>> 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);
> Please add "extern" to the function declaration to be consistent with
> other functional declarations in mutex.h.
'extern' is pointless and deprecated on function prototypes. Already
having some is not a good reason to add new ones, errors from the past
should be avoided nowadays. With time they should all disappear so don't
add new ones.
>> +
>> +#else
>> +
>> +static inline int devm_mutex_init(struct device *dev, struct mutex
>> *lock)
>> +{
>> + mutex_init(lock);
>> + return 0;
>> +}
>
> I would prefer you to add a devm_mutex_init macro after the function
> declaration and put this inline function at the end of header if the
> devm_mutex_init macro isn't defined. In this way, you don't need to
> repeat this inline function twice as it has no dependency on PREEMPT_RT.
It is already done that way for other functions in that file. Should be
kept consistant. I agree with you it is not ideal, maybe we should
rework that file completely but I don't like the idea of a
devm_mutex_init macro for that.
Christophe
>
> By doing this, you can also move the function declaration right after
> mutex_destroy() without the need to add another #ifdef
> CONFIG_DEBUG_MUTEXES block.
>
>> +
>> +#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);
>
> The mutex-debug.c change looks fine to me.
>
> Cheers,
> Longman
>
>
On 12/14/23 14:53, Christophe Leroy wrote:
>
> Le 14/12/2023 à 19:48, Waiman Long a écrit :
>> On 12/14/23 12:36, 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 <[email protected]>
>>> ---
>>> 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);
>> Please add "extern" to the function declaration to be consistent with
>> other functional declarations in mutex.h.
> 'extern' is pointless and deprecated on function prototypes. Already
> having some is not a good reason to add new ones, errors from the past
> should be avoided nowadays. With time they should all disappear so don't
> add new ones.
Yes, "extern" is optional. It is just a suggestion and I am going to
argue about that.
>
>>> +
>>> +#else
>>> +
>>> +static inline int devm_mutex_init(struct device *dev, struct mutex
>>> *lock)
>>> +{
>>> + mutex_init(lock);
>>> + return 0;
>>> +}
>> I would prefer you to add a devm_mutex_init macro after the function
>> declaration and put this inline function at the end of header if the
>> devm_mutex_init macro isn't defined. In this way, you don't need to
>> repeat this inline function twice as it has no dependency on PREEMPT_RT.
> It is already done that way for other functions in that file. Should be
> kept consistant. I agree with you it is not ideal, maybe we should
> rework that file completely but I don't like the idea of a
> devm_mutex_init macro for that.
devm_mutex_init() is not an API for the core mutex code. That is why I
want to minimize change to the existing code layout. Putting it at the
end will reduce confusion when developers look up mutex.h header file to
find out what mutex functions are available.
Cheers,
Longman
Le 14/12/2023 à 22:48, Waiman Long a écrit :
> On 12/14/23 14:53, Christophe Leroy wrote:
>>
>> Le 14/12/2023 à 19:48, Waiman Long a écrit :
>>> On 12/14/23 12:36, 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 <[email protected]>
>>>> ---
>>>> 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);
>>> Please add "extern" to the function declaration to be consistent with
>>> other functional declarations in mutex.h.
>> 'extern' is pointless and deprecated on function prototypes. Already
>> having some is not a good reason to add new ones, errors from the past
>> should be avoided nowadays. With time they should all disappear so don't
>> add new ones.
> Yes, "extern" is optional. It is just a suggestion and I am going to
> argue about that.
FWIW, note that when you perform a strict check with checkpatch.pl, you
get a warning for that:
$ ./scripts/checkpatch.pl --strict -g HEAD
CHECK: extern prototypes should be avoided in .h files
#56: FILE: include/linux/mutex.h:131:
+extern int devm_mutex_init(struct device *dev, struct mutex *lock);
total: 0 errors, 0 warnings, 1 checks, 99 lines checked
>>
>>>> +
>>>> +#else
>>>> +
>>>> +static inline int devm_mutex_init(struct device *dev, struct mutex
>>>> *lock)
>>>> +{
>>>> + mutex_init(lock);
>>>> + return 0;
>>>> +}
>>> I would prefer you to add a devm_mutex_init macro after the function
>>> declaration and put this inline function at the end of header if the
>>> devm_mutex_init macro isn't defined. In this way, you don't need to
>>> repeat this inline function twice as it has no dependency on PREEMPT_RT.
>> It is already done that way for other functions in that file. Should be
>> kept consistant. I agree with you it is not ideal, maybe we should
>> rework that file completely but I don't like the idea of a
>> devm_mutex_init macro for that.
>
> devm_mutex_init() is not an API for the core mutex code. That is why I
> want to minimize change to the existing code layout. Putting it at the
> end will reduce confusion when developers look up mutex.h header file to
> find out what mutex functions are available.
If I look at linux/gpio.h we are more or less in the same situation I think.
devm_mutex_init() is not an API for the core mutex code, but developers
need to know the managed functions for mutex exist, and having them at
the same place as non managed functions looks better to me. Now I agree
with you that this duplication of functions is not the best, and it also
applies to existing content of mutex.h so maybe we can do something
about it later and improve the situation.
Christophe
Hello Christophe
On 12/15/23 08:46, Christophe Leroy wrote:
>
>
> Le 14/12/2023 à 22:48, Waiman Long a écrit :
>> On 12/14/23 14:53, Christophe Leroy wrote:
>>>
>>> Le 14/12/2023 à 19:48, Waiman Long a écrit :
>>>> On 12/14/23 12:36, 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 <[email protected]>
>>>>> ---
>>>>> 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);
>>>> Please add "extern" to the function declaration to be consistent with
>>>> other functional declarations in mutex.h.
>>> 'extern' is pointless and deprecated on function prototypes. Already
>>> having some is not a good reason to add new ones, errors from the past
>>> should be avoided nowadays. With time they should all disappear so don't
>>> add new ones.
>> Yes, "extern" is optional. It is just a suggestion and I am going to
>> argue about that.
>
> FWIW, note that when you perform a strict check with checkpatch.pl, you
> get a warning for that:
>
> $ ./scripts/checkpatch.pl --strict -g HEAD
> CHECK: extern prototypes should be avoided in .h files
> #56: FILE: include/linux/mutex.h:131:
> +extern int devm_mutex_init(struct device *dev, struct mutex *lock);
>
> total: 0 errors, 0 warnings, 1 checks, 99 lines checked
This is ambiguous situation about extern. It's deprecated and useless on
one hand but harmless. And those externs will not disappear by themself
- it'll be one patch that clean them all at once (in one header at
least) so one more extern will not alter the overall picture.
On the other hand if we manage to place devm_mutex_init near
mutex_destroy then we'll have:
int devm_mutex_init(struct device *dev, struct mutex *lock);
extern void mutex_destroy(struct mutex *lock);
and it raises questions and does not look very nice.
>>>
>>>>> +
>>>>> +#else
>>>>> +
>>>>> +static inline int devm_mutex_init(struct device *dev, struct mutex
>>>>> *lock)
>>>>> +{
>>>>> + mutex_init(lock);
>>>>> + return 0;
>>>>> +}
>>>> I would prefer you to add a devm_mutex_init macro after the function
>>>> declaration and put this inline function at the end of header if the
>>>> devm_mutex_init macro isn't defined. In this way, you don't need to
>>>> repeat this inline function twice as it has no dependency on PREEMPT_RT.
>>> It is already done that way for other functions in that file. Should be
>>> kept consistant. I agree with you it is not ideal, maybe we should
>>> rework that file completely but I don't like the idea of a
>>> devm_mutex_init macro for that.
>>
>> devm_mutex_init() is not an API for the core mutex code. That is why I
>> want to minimize change to the existing code layout. Putting it at the
>> end will reduce confusion when developers look up mutex.h header file to
>> find out what mutex functions are available.
>
> If I look at linux/gpio.h we are more or less in the same situation I think.
>
> devm_mutex_init() is not an API for the core mutex code, but developers
> need to know the managed functions for mutex exist, and having them at
> the same place as non managed functions looks better to me. Now I agree
> with you that this duplication of functions is not the best, and it also
> applies to existing content of mutex.h so maybe we can do something
> about it later and improve the situation.
>
> Christophe
--
Best regards
George
Le 17/12/2023 à 02:05, George Stark a écrit :
> [Vous ne recevez pas souvent de courriers de [email protected].
> Découvrez pourquoi ceci est important à
> https://aka.ms/LearnAboutSenderIdentification ]
>
> Hello Christophe
>
> On 12/15/23 08:46, Christophe Leroy wrote:
>>
>>
>> Le 14/12/2023 à 22:48, Waiman Long a écrit :
>>> On 12/14/23 14:53, Christophe Leroy wrote:
>>>>
>>>> Le 14/12/2023 à 19:48, Waiman Long a écrit :
>>>>> On 12/14/23 12:36, 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 <[email protected]>
>>>>>> ---
>>>>>> 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);
>>>>> Please add "extern" to the function declaration to be consistent with
>>>>> other functional declarations in mutex.h.
>>>> 'extern' is pointless and deprecated on function prototypes. Already
>>>> having some is not a good reason to add new ones, errors from the past
>>>> should be avoided nowadays. With time they should all disappear so
>>>> don't
>>>> add new ones.
>>> Yes, "extern" is optional. It is just a suggestion and I am going to
>>> argue about that.
>>
>> FWIW, note that when you perform a strict check with checkpatch.pl, you
>> get a warning for that:
>>
>> $ ./scripts/checkpatch.pl --strict -g HEAD
>> CHECK: extern prototypes should be avoided in .h files
>> #56: FILE: include/linux/mutex.h:131:
>> +extern int devm_mutex_init(struct device *dev, struct mutex *lock);
>>
>> total: 0 errors, 0 warnings, 1 checks, 99 lines checked
>
> This is ambiguous situation about extern. It's deprecated and useless on
> one hand but harmless. And those externs will not disappear by themself
> - it'll be one patch that clean them all at once (in one header at
> least) so one more extern will not alter the overall picture.
That kind of cleanup patch bomb is a nightmare for backporting, so if it
happens one day it should be as light as possible, hence the importance
to not add new ones and remove existing one everytime you modify or move
a line including it for whatever reason.
>
> On the other hand if we manage to place devm_mutex_init near
> mutex_destroy then we'll have:
>
> int devm_mutex_init(struct device *dev, struct mutex *lock);
> extern void mutex_destroy(struct mutex *lock);
I sent you an alternative proposal that avoids duplication of the static
inline version of devm_mutex_init(). If you agree with it just take it
into your series and that question will vanish.
>
> and it raises questions and does not look very nice.
If you look at linux/mm.h there are plenty of them anyway, so why do
different ? For an exemple look at
https://elixir.bootlin.com/linux/v6.7-rc4/source/include/linux/mm.h#L2372
Christophe
Hello Christophe
On 12/17/23 12:31, Christophe Leroy wrote:
...
>>>>>>> ---
>>>>>>> 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);
>>>>>> Please add "extern" to the function declaration to be consistent with
>>>>>> other functional declarations in mutex.h.
>>>>> 'extern' is pointless and deprecated on function prototypes. Already
>>>>> having some is not a good reason to add new ones, errors from the past
>>>>> should be avoided nowadays. With time they should all disappear so
>>>>> don't
>>>>> add new ones.
>>>> Yes, "extern" is optional. It is just a suggestion and I am going to
>>>> argue about that.
>>>
>>> FWIW, note that when you perform a strict check with checkpatch.pl, you
>>> get a warning for that:
>>>
>>> $ ./scripts/checkpatch.pl --strict -g HEAD
>>> CHECK: extern prototypes should be avoided in .h files
>>> #56: FILE: include/linux/mutex.h:131:
>>> +extern int devm_mutex_init(struct device *dev, struct mutex *lock);
>>>
>>> total: 0 errors, 0 warnings, 1 checks, 99 lines checked
>>
>> This is ambiguous situation about extern. It's deprecated and useless on
>> one hand but harmless. And those externs will not disappear by themself
>> - it'll be one patch that clean them all at once (in one header at
>> least) so one more extern will not alter the overall picture.
>
> That kind of cleanup patch bomb is a nightmare for backporting, so if it
> happens one day it should be as light as possible, hence the importance
> to not add new ones and remove existing one everytime you modify or move
> a line including it for whatever reason.
>
>>
>> On the other hand if we manage to place devm_mutex_init near
>> mutex_destroy then we'll have:
>>
>> int devm_mutex_init(struct device *dev, struct mutex *lock);
>> extern void mutex_destroy(struct mutex *lock);
>
> I sent you an alternative proposal that avoids duplication of the static
> inline version of devm_mutex_init(). If you agree with it just take it
> into your series and that question will vanish.
Thanks for that patch by the way. The only comment is that moving
mutex_destroy
should be done in a separate patch IMO.
Waiman Long proposed such a refactoring here:
https://lore.kernel.org/lkml/[email protected]/T/
With this patch adding devm_mutex_init would be straightforward.
>>
>> and it raises questions and does not look very nice.
>
> If you look at linux/mm.h there are plenty of them anyway, so why do
> different ? For an exemple look at
> https://elixir.bootlin.com/linux/v6.7-rc4/source/include/linux/mm.h#L2372
Oh, I see. Ok, I don't have any more arguments against removing extern.
We'll see what mutex.h maintainers decide.
>
> Christophe
--
Best regards
George