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

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Message-ID: <84568b5e-4e6b-4c6e-b5d0-ba77d8fe087b@igalia.com>
Date: Mon, 3 Feb 2025 11:16:31 -0300
From: André Almeida <andrealmeid@...lia.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>, Florian Weimer
 <fweimer@...hat.com>, 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

Em 03/02/2025 10:29, Peter Zijlstra escreveu:
> 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.
> 

Oh, now I see, thanks for the clarification. I will add this for the new 
interface then.

In the meanwhile, if you can a look at  patch 3/4 "selftests/futex: 
Create test for robust list" that would help to make sure the new 
interface don't mess with the old one.