linux-kernel - Re: [PATCH -next] x86/mm/pat: silence a data race in cpa_4k

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Date:   Tue, 21 Jan 2020 16:45:28 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Marco Elver <elver@...gle.com>, Qian Cai <cai@....pw>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next] x86/mm/pat: silence a data race in cpa_4k_install

On Tue, Jan 21, 2020 at 04:36:49PM +0100, Marco Elver wrote:
> Isn't the intent "x86/mm/pat: Mark intentional data race" ?  The fact
> that KCSAN no longer shows the warning is a side-effect.  At least
> that's how I see it.

Perhaps because you've been dealing with KCSAN for so long. :-)

The main angle here, IMO, is that this "fix" is being done solely for
KCSAN. Or is there another reason to "fix" intentional data races? At
least I don't see one. And the text says

"This will generate a lot of noise on a debug kernel with
debug_pagealloc with KCSAN enabled which could render the system
unusable."

So yes, I think it should say something about making KCSAN happy.

Oh, and while at it I'd prefer it if it did the __no_kcsan function
annotation instead of the data_race() thing.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette