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

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Date:   Wed, 13 May 2020 14:32:43 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Marco Elver <elver@...gle.com>
Cc:     Will Deacon <will@...nel.org>, 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 Wed, May 13, 2020 at 01:48:41PM +0200, Marco Elver wrote:

> Disabling most instrumentation for arch/x86 is reasonable. Also fine
> with the __READ_ONCE/__WRITE_ONCE changes (your improved
> compiler-friendlier version).
> 
> We likely can't have both: still instrument __READ_ONCE/__WRITE_ONCE
> (as Will suggested) *and* avoid double-instrumentation in arch_atomic.
> If most use-cases of __READ_ONCE/__WRITE_ONCE are likely to use
> data_race() or KCSAN_SANITIZE := n anyway, I'd say it's reasonable for
> now.

Right, if/when people want sanitize crud enabled for x86 I need
something that:

 - can mark a function 'no_sanitize' and all code that gets inlined into
   that function must automagically also not get sanitized. ie. make
   inline work like macros (again).

And optionally:

 - can mark a function explicitly 'sanitize', and only when an explicit
   sanitize and no_sanitize mix in inlining give the current
   incompatible attribute splat.

That way we can have the noinstr function attribute imply no_sanitize
and frob the DEFINE_IDTENTRY*() macros to use (a new) sanitize_or_inline
helper instead of __always_inline for __##func().