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

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Message-ID: <20241008180911.JiqZxSLg@linutronix.de>
Date: Tue, 8 Oct 2024 20:09:11 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: André Almeida <andrealmeid@...lia.com>
Cc: Juri Lelli <juri.lelli@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, Darren Hart <dvhart@...radead.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Valentin Schneider <vschneid@...hat.com>,
	Waiman Long <longman@...hat.com>
Subject: Re: Futex hash_bucket lock can break isolation and cause priority
 inversion on RT

On 2024-10-08 12:59:24 [-0300], André Almeida wrote:
> 
> So if every process has it owns hb-lock, every process has their own bucket?
> It would act just like a linked list then?

If you have one hb-lock, yes. But you could have 4 or 8 slots. A slot
has 64 bytes due to alignment. As-is the 8 slots would occupy 512 bytes
of memory.

Sebastian