Re: [PATCH v3 06/14] locking/mutex: Expose mutex_owner()

Peter Zijlstra
2023-04-22T10:36:42Z

On Tue, Apr 11, 2023 at 04:25:03AM +0000, John Stultz wrote:

> include/linux/mutex.h | 2 ++
> kernel/locking/mutex.c | 5 +++++
> 2 files changed, 7 insertions(+)
>
> diff --git a/include/linux/mutex.h b/include/linux/mutex.h
> index 8f226d460f51..ebdc59cb0bf6 100644
> --- a/include/linux/mutex.h
> +++ b/include/linux/mutex.h
> @@ -118,6 +118,8 @@ do { \
> extern void __mutex_init(struct mutex *lock, const char *name,
> struct lock_class_key *key);
>
> +extern struct task_struct *mutex_owner(struct mutex *lock);
> +
> /**
> * mutex_is_locked - is the mutex locked
> * @lock: the mutex to be queried
> diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
> index 45f1b7519f63..cbc34d5f4486 100644
> --- a/kernel/locking/mutex.c
> +++ b/kernel/locking/mutex.c
> @@ -81,6 +81,11 @@ static inline struct task_struct *__mutex_owner(struct mutex *lock)
> return (struct task_struct *)(atomic_long_read(&lock->owner) & ~MUTEX_FLAGS);
> }
>
> +struct task_struct *mutex_owner(struct mutex *lock)
> +{
> + return __mutex_owner(lock);
> +}
> +
> static inline struct task_struct *__owner_task(unsigned long owner)
> {
> return (struct task_struct *)(owner & ~MUTEX_FLAGS);

Urgh, no.

It exposes mutex_owner() far wider than it should be, and also it turns
what should be a simple load into a function call :/

Looking at the lastest patches I have here this used to be an inline in
kernel/locking/mutex.h and kernel/sched/core.c got to #include
"../locking/mutex.h".