linux-kernel - Re: Futex hash_bucket lock can break isolation and cause priority inversion on RT

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Message-ID: <5f125ed8-66bb-4654-b1da-b8db643b81d6@redhat.com>
Date: Tue, 8 Oct 2024 15:44:23 -0400
From: Waiman Long <llong@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Darren Hart <dvhart@...radead.org>, Davidlohr Bueso <dave@...olabs.net>,
 André Almeida <andrealmeid@...lia.com>,
 LKML <linux-kernel@...r.kernel.org>,
 linux-rt-users <linux-rt-users@...r.kernel.org>,
 Valentin Schneider <vschneid@...hat.com>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 Juri Lelli <juri.lelli@...hat.com>
Subject: Re: Futex hash_bucket lock can break isolation and cause priority
 inversion on RT


On 10/8/24 1:38 PM, Peter Zijlstra wrote:
> On Tue, Oct 08, 2024 at 04:22:26PM +0100, Juri Lelli wrote:
>> Does this report make any sense? If it does, has this issue ever been
>> reported and possibly discussed? I guess it’s kind of a corner case, but
>> I wonder if anybody has suggestions already on how to possibly try to
>> tackle it from a kernel perspective.
> Any shared lock can cause such havoc. Futex hash buckets is just one of
> a number of very popular ones that's relatively easy to hit.
>
> I do have some futex-numa patches still pending, but they won't
> magically sure this either. Userspace needs help at the very least.

Regarding the futex-numa patches, are you planning to get them merged 
soon? We have customers asking for that.

Cheers,
Longman