linux-kernel - Re: [PATCH v6 0/9] futex: Create {set,get}_robust

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Message-ID: <32cbcdbf-c98e-4075-b5cd-a7e001de05b3@igalia.com>
Date: Sat, 22 Nov 2025 11:25:44 -0300
From: André Almeida <andrealmeid@...lia.com>
To: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Peter Zijlstra <peterz@...radead.org>, Darren Hart <dvhart@...radead.org>,
 Davidlohr Bueso <dave@...olabs.net>, Arnd Bergmann <arnd@...db.de>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 Waiman Long <longman@...hat.com>, Ryan Houdek <Sonicadvance1@...il.com>
Cc: linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
 linux-api@...r.kernel.org, kernel-dev@...lia.com
Subject: Re: [PATCH v6 0/9] futex: Create {set,get}_robust_list2() syscalls

Em 22/11/2025 02:50, André Almeida escreveu:
> Hello,
> 
> This version is a complete rewrite of the syscall (thanks Thomas for the
> suggestions!).
> 
>   * Use case
> 
> The use-case for the new syscalls is detailed in the last patch version:
> 
>    https://lore.kernel.org/lkml/20250626-tonyk-robust_futex-v5-0-179194dbde8f@igalia.com
> 
>   * The syscall interface
> 
> Documented at patches 3/9 "futex: Create set_robust_list2() syscall" and
> 4/9 "futex: Create get_robust_list2() syscall".
> 
>   * Testing
> 
> I expanded the current robust list selftest to use the new interface,
> and also ported the original syscall to use the new syscall internals,
> and everything survived the tests.
> 
>   * Changelog
> 
> Changes from v5:
>   - Complete interface rewrite, there are so many changes but the main
>     ones are the following points
>   - Array of robust lists now has a static size, allocated once during the
>     first usage of the list
>   - Now that the list of robust lists have a fixed size, I removed the
>     logic of having a command for creating a new index on the list. To
>     simplify things for everyone, userspace just need to call
>     set_robust_list2(head, 32-bit/64-bit type, index).

Actually, this won't work well. The application that calls 
set_robust_list2() may be using glibc, that will also want to call 
set_robust_list2(), and there's no way to know which lists are being by 
each library. I will re-add the create/modify logic for the next version.