linux-kernel - Re: [tip:locking/urgent] compiler, atomics: Provide READ_ONCE

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Message-ID: <20151014165451.GV3604@twins.programming.kicks-ass.net>
Date:	Wed, 14 Oct 2015 18:54:51 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Dmitry Vyukov <dvyukov@...gle.com>
Cc:	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	tip-bot for Andrey Ryabinin <tipbot@...or.com>,
	linux-tip-commits@...r.kernel.org,
	kasan-dev <kasan-dev@...glegroups.com>,
	Ingo Molnar <mingo@...nel.org>,
	Kostya Serebryany <kcc@...gle.com>,
	Borislav Petkov <bp@...en8.de>,
	Andrey Ryabinin <aryabinin@...tuozzo.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sasha Levin <sasha.levin@...cle.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Wolfram Gloger <wmglo@...t.med.uni-muenchen.de>,
	Andrey Konovalov <andreyknvl@...gle.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Alexander Potapenko <glider@...gle.com>
Subject: Re: [tip:locking/urgent] compiler, atomics: Provide
 READ_ONCE_NOCHECK ()

On Wed, Oct 14, 2015 at 06:34:16PM +0200, Dmitry Vyukov wrote:
> On Wed, Oct 14, 2015 at 6:20 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Wed, Oct 14, 2015 at 06:18:58PM +0200, Dmitry Vyukov wrote:
> >>
> >> Well, if another thread writes it byte-by-byte, it pretty much does
> >> not matter how you read it.
> >> Note that I said "at least one access is not atomic". If both are
> >> atomic, then this is, of course, legal. And KTSAN considers
> >> READ/WRITE_ONCE as atomic operations.
> >
> > OK, then I'm confused on what exactly the annotation does, but less
> > worried.
> 
> The plan is to make READ_ONCE_NOCHECK ignored by KTSAN, just it is
> ignored by KASAN. So that it never leads to a report ("not checked").

Would a _NOKSAN suffix not be more appropriate? NOCHECK seems somewhat
generic.
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