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

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Message-ID: <20241105121009.GH24862@noisy.programming.kicks-ass.net>
Date: Tue, 5 Nov 2024 13:10:09 +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 Mon, Nov 04, 2024 at 06:55:45PM -0300, André Almeida wrote:
> Hi Peter,
> 
> Em 04/11/2024 08:22, Peter Zijlstra escreveu:
> > 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.
> > 
> 
> You are asking if, whenever someone calls set_robust_list() or
> compat_set_robust_list() to be inserted into &current->robust_list2 instead
> of using tsk->robust_list and tsk->compat_robust_list?

Yes, that.