Re: [PATCH v5 1/3] hung_task: replace blocker_mutex with encoded blocker

[Andrew Morton]

On Mon, 14 Apr 2025 22:59:43 +0800 Lance Yang <ioworker0@xxxxxxxxx> wrote:

> This patch replaces 'struct mutex *blocker_mutex' with 'unsigned long
> blocker', as only one blocker is active at a time.
> 
> The blocker filed can store both the lock addrees and the lock type, with
> LSB used to encode the type as Masami suggested, making it easier to extend
> the feature to cover other types of locks.
> 
> Also, once the lock type is determined, we can directly extract the address
> and cast it to a lock pointer ;)
> 
> ...
>
>  static void debug_show_blocker(struct task_struct *task)
>  {
>  	struct task_struct *g, *t;
> -	unsigned long owner;
> -	struct mutex *lock;
> +	unsigned long owner, blocker;
>  
>  	RCU_LOCKDEP_WARN(!rcu_read_lock_held(), "No rcu lock held");
>  
> -	lock = READ_ONCE(task->blocker_mutex);
> -	if (!lock)
> +	blocker = READ_ONCE(task->blocker);
> +	if (!blocker ||
> +	    hung_task_get_blocker_type(blocker) != BLOCKER_TYPE_MUTEX)
>  		return;
>  
> -	owner = mutex_get_owner(lock);
> +	owner = mutex_get_owner(
> +		(struct mutex *)hung_task_blocker_to_lock(blocker));

typecast is unneeded?