linux-kernel - Re: [PATCH v2 2/3] futex: Create set_robust

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Message-ID: <20241104112240.GA24862@noisy.programming.kicks-ass.net>
Date: Mon, 4 Nov 2024 12:22:40 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: André Almeida <andrealmeid@...lia.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Darren Hart <dvhart@...radead.org>,
	Davidlohr Bueso <dave@...olabs.net>, Arnd Bergmann <arnd@...db.de>,
	sonicadvance1@...il.com, linux-kernel@...r.kernel.org,
	kernel-dev@...lia.com, linux-api@...r.kernel.org,
	Nathan Chancellor <nathan@...nel.org>
Subject: Re: [PATCH v2 2/3] futex: Create set_robust_list2

On Fri, Nov 01, 2024 at 01:21:46PM -0300, André Almeida wrote:
> @@ -1046,24 +1095,44 @@ static inline void exit_pi_state_list(struct task_struct *curr) { }
>  
>  static void futex_cleanup(struct task_struct *tsk)
>  {
> +	struct robust_list2_entry *curr, *n;
> +	struct list_head *list2 = &tsk->robust_list2;
> +
>  #ifdef CONFIG_64BIT
>  	if (unlikely(tsk->robust_list)) {
> -		exit_robust_list64(tsk);
> +		exit_robust_list64(tsk, tsk->robust_list);
>  		tsk->robust_list = NULL;
>  	}
>  #else
>  	if (unlikely(tsk->robust_list)) {
> -		exit_robust_list32(tsk);
> +		exit_robust_list32(tsk, (struct robust_list_head32 *) tsk->robust_list);
>  		tsk->robust_list = NULL;
>  	}
>  #endif
>  
>  #ifdef CONFIG_COMPAT
>  	if (unlikely(tsk->compat_robust_list)) {
> -		exit_robust_list32(tsk);
> +		exit_robust_list32(tsk, tsk->compat_robust_list);
>  		tsk->compat_robust_list = NULL;
>  	}
>  #endif
> +	/*
> +	 * Walk through the linked list, parsing robust lists and freeing the
> +	 * allocated lists
> +	 */
> +	if (unlikely(!list_empty(list2))) {
> +		list_for_each_entry_safe(curr, n, list2, list) {
> +			if (curr->head != NULL) {
> +				if (curr->list_type == ROBUST_LIST_64BIT)
> +					exit_robust_list64(tsk, curr->head);
> +				else if (curr->list_type == ROBUST_LIST_32BIT)
> +					exit_robust_list32(tsk, curr->head);
> +				curr->head = NULL;
> +			}
> +			list_del_init(&curr->list);
> +			kfree(curr);
> +		}
> +	}
>  
>  	if (unlikely(!list_empty(&tsk->pi_state_list)))
>  		exit_pi_state_list(tsk);

I'm still digesting this, but the above seems particularly silly.

Should not the legacy lists also be on the list of lists? I mean, it
makes no sense to have two completely separate means of tracking lists.