linux-kernel - Re: [PATCH] stop_machine: avoid potential race behaviour

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Message-ID: <20191008083637.GI2294@hirez.programming.kicks-ass.net>
Date:   Tue, 8 Oct 2019 10:36:37 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-kernel@...r.kernel.org, Marco Elver <elver@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] stop_machine: avoid potential race behaviour

On Mon, Oct 07, 2019 at 11:45:36AM +0100, Mark Rutland wrote:
> Both multi_cpu_stop() and set_state() access multi_stop_data::state
> racily using plain accesses. These are subject to compiler
> transformations which could break the intended behaviour of the code,
> and this situation is detected by KCSAN on both arm64 and x86 (splats
> below).

I really don't think there is anything the compiler can do wrong here.

That is, I'm thinking I'd like to get this called out as a false-positive.

That said, the patch looks obviously fine and will help with the
validation effort so no real objection there.