Re: [PATCH v2] locking/rtmutex: Annotate API and implementation

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2026-05-05 04:26:44 [+0200], Bart Van Assche wrote:
> --- a/include/linux/rtmutex.h
> +++ b/include/linux/rtmutex.h
> @@ -56,6 +56,8 @@ static inline struct task_struct *rt_mutex_owner(struct rt_mutex_base *lock)
>  #endif
>  extern void rt_mutex_base_init(struct rt_mutex_base *rtb);
>  
> +context_lock_struct(rt_mutex);

What does this do? Shouldn't this define the struct?

>  /**
>   * The rt_mutex structure
>   *
> @@ -108,8 +110,10 @@ do { \
>  extern void __rt_mutex_init(struct rt_mutex *lock, const char *name, struct lock_class_key *key);
>  
>  #ifdef CONFIG_DEBUG_LOCK_ALLOC
> -extern void rt_mutex_lock_nested(struct rt_mutex *lock, unsigned int subclass);
> -extern void _rt_mutex_lock_nest_lock(struct rt_mutex *lock, struct lockdep_map *nest_lock);
> +extern void rt_mutex_lock_nested(struct rt_mutex *lock, unsigned int subclass)
> +	__acquires(lock);
> +extern void _rt_mutex_lock_nest_lock(struct rt_mutex *lock, struct lockdep_map *nest_lock)
> +	__acquires(lock);
>  #define rt_mutex_lock(lock) rt_mutex_lock_nested(lock, 0)
>  #define rt_mutex_lock_nest_lock(lock, nest_lock)			\
>  	do {								\
> @@ -118,15 +122,19 @@ extern void _rt_mutex_lock_nest_lock(struct rt_mutex *lock, struct lockdep_map *
>  	} while (0)
>  
>  #else
> -extern void rt_mutex_lock(struct rt_mutex *lock);
> +extern void rt_mutex_lock(struct rt_mutex *lock) __acquires(lock);

So this is "one" thing where you add annotation to the rt_mutex*() API
for external users. Then you add the wait_lock annotation. Different
scope but okay.

…
> --- a/kernel/locking/rtmutex_api.c
> +++ b/kernel/locking/rtmutex_api.c
> @@ -66,12 +67,14 @@ EXPORT_SYMBOL(rt_mutex_base_init);
>   * @subclass: the lockdep subclass
>   */
>  void __sched rt_mutex_lock_nested(struct rt_mutex *lock, unsigned int subclass)
> +	__no_context_analysis /* ignoring the return value below is fine in this case */
>  {
>  	__rt_mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, NULL, subclass);
>  }
>  EXPORT_SYMBOL_GPL(rt_mutex_lock_nested);
>  
>  void __sched _rt_mutex_lock_nest_lock(struct rt_mutex *lock, struct lockdep_map *nest_lock)
> +	__no_context_analysis /* ignoring the return value below is fine in this case */
>  {
>  	__rt_mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, nest_lock, 0);
>  }

*Why* is it okay? Because the void always acquire the lock and only the
conditional locking (which can be interrupted by signal/ timeout) return
an error if they failed to acquire the lock. Something like that would
be nice for the comment.

Not sure if "__no_context_analysis" is the right thing to do here.
  __acquires(lock) __no_context_analysis

might be better if just __acquires leads to trouble.

Sebastian