linux-kernel - Re: [PATCH v2 0/4] futex: Drop ROBUST_LIST

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Message-ID: <20250203132926.GE14028@noisy.programming.kicks-ass.net>
Date: Mon, 3 Feb 2025 14:29:26 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Florian Weimer <fweimer@...hat.com>
Cc: André Almeida <andrealmeid@...lia.com>,
	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>,
	linux-kernel@...r.kernel.org, kernel-dev@...lia.com,
	Vinicius Peixoto <vpeixoto@...amp.dev>
Subject: Re: [PATCH v2 0/4] futex: Drop ROBUST_LIST_LIMIT

On Tue, Jan 28, 2025 at 08:50:41AM +0100, Florian Weimer wrote:
> * André Almeida:
> 
> > As requested by Peter at [1], this patchset drops the
> > ROBUST_LIST_LIMIT. This is achieve by simply rewriting the processed
> > list element ->next to point to the head->list address, destroying the
> > linked list to avoid any circular list.

Well, I suggested we do this for a new robust list.

> Furthermore, I'm not entirely sure
> if this is entirely backwards-compatible.

I share Florian's concern about backward compat here. It might work, it
might not.

I was just saying that if we're going to be doing new robust lists, we
should try and fix all the known wrongs, and this one lets us get rid of the limit.

> Could you use the tortoise/hare approach instead?

That seems overly complicated for what we need.