linux-kernel - Re: [PATCH v5 00/18] Rework READ

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Message-ID: <20200514135639.GA2978@hirez.programming.kicks-ass.net>
Date:   Thu, 14 May 2020 15:56:39 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Marco Elver <elver@...gle.com>
Cc:     Will Deacon <will@...nel.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v5 00/18] Rework READ_ONCE() to improve codegen

On Thu, May 14, 2020 at 03:35:58PM +0200, Marco Elver wrote:

>   5. we should not break atomic_{read,set} for KCSAN. [Because of #1,
> we'd need to add data_race() around the arch-calls in
> atomic_{read,set}; or rely on Clang 11's -tsan-distinguish-volatile
> support (GCC 11 might get this as well).]

Putting the data_race() in atomic_{read,set} would 'break' any sanitized
user of arch_atomic_{read,set}(). Now it so happens there aren't any
such just now, but we need to be aware of that.

I'm thinking the volatile thing is the nicest solution, but yes, that'll
make us depend on 11 everything.