Re: [PATCH sched_ext/for-7.2] sched_ext: add p->scx.tid and SCX_OPS_TID_TO_TASK lookup

[Cheng-Yang Chou <yphbchou0911@gmail.com>]

Hi Tejun, sorry for the noise

On Sun, Apr 19, 2026 at 06:18:46AM -1000, Tejun Heo wrote:
[snipped]
>  void scx_pre_fork(struct task_struct *p)
>  {
>  	/*
> @@ -3682,6 +3732,8 @@ int scx_fork(struct task_struct *p, stru
>  
>  	percpu_rwsem_assert_held(&scx_fork_rwsem);
>  
> +	p->scx.tid = scx_alloc_tid();
> +
>  	if (scx_init_task_enabled) {
>  #ifdef CONFIG_EXT_SUB_SCHED
>  		struct scx_sched *sch = kargs->cset->dfl_cgrp->scx_sched;
> @@ -3717,9 +3769,13 @@ void scx_post_fork(struct task_struct *p
>  		}
>  	}
>  
> -	raw_spin_lock_irq(&scx_tasks_lock);
> -	list_add_tail(&p->scx.tasks_node, &scx_tasks);
> -	raw_spin_unlock_irq(&scx_tasks_lock);
> +	scoped_guard(raw_spinlock_irq, &scx_tasks_lock) {
> +		list_add_tail(&p->scx.tasks_node, &scx_tasks);
> +		if (scx_tid_to_task_enabled())
> +         rhashtable_lookup_insert_fast(&scx_tid_hash,

After reading the review from Sashiko [1], should we handle insertion
failures here?

	ret = rhashtable_lookup_insert_fast()
	if(unlikely(ret))
		scx_error(...)

> +						      &p->scx.tid_hash_node,
> +						      scx_tid_hash_params);
> +	}
>  
>  	percpu_up_read(&scx_fork_rwsem);
>  }

[...]
> +		/*
> +		 * Insert into the tid hash under scx_tasks_lock so we can't
> +		 * race sched_ext_dead() and leave a stale entry for an already
> +		 * exited task.
> +		 */
> +		if (scx_tid_to_task_enabled()) {
> +			guard(raw_spinlock_irq)(&scx_tasks_lock);
> +			if (!list_empty(&p->scx.tasks_node))
> +				rhashtable_lookup_insert_fast(&scx_tid_hash,

Same here, thanks.

> +							      &p->scx.tid_hash_node,
> +							      scx_tid_hash_params);
> +		}
> +
>  		put_task_struct(p);
>  	}

[1]: https://sashiko.dev/#/patchset/a19c8c74d7c767bc9865b75d6de7c723%40kernel.org

-- 
Cheers,
Cheng-Yang