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Date: Mon, 20 Nov 2017 12:53:50 -0800
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: [PATCH v2 18/18] arm64: select ARCH_SUPPORTS_LTO_CLANG
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To: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will.deacon@arm.com>, Sami Tolvanen <samitolvanen@google.com>, Nick Desaulniers <ndesaulniers@google.com>, Alex Matveev <alxmtvv@gmail.com>, Andi Kleen <ak@linux.intel.com>, Ard Biesheuvel <ard.biesheuvel@linaro.org>, Greg Hackmann <ghackmann@google.com>, Kees Cook <keescook@chromium.org>, linux-arm-kernel@lists.infradead.org, Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>, Mark Rutland <mark.rutland@arm.com>, Masahiro Yamada <yamada.masahiro@socionext.com>, Maxim Kuvyrkov <maxim.kuvyrkov@linaro.org>, Michal Marek <michal.lkml@markovi.net>, Yury Norov <ynorov@caviumnetworks.com>, Matthias Kaehlcke <mka@chromium.org>, Alexander Potapenko <glider@google.com>, Stephen Hines <srhines@google.com>, Pirama Arumuga Nainar <pirama@google.com>, Manoj Gupta <manojgupta@google.com>

On Mon, Nov 20, 2017 at 08:32:56PM +0100, Peter Zijlstra wrote:
> On Mon, Nov 20, 2017 at 06:05:55PM +0000, Will Deacon wrote:
> > Although the current direction of the C++ committee is to prefer
> > that dependencies are explicitly "marked", this is not deemed to be
> > acceptable for the kernel (in other words, everything is always considered
> > "marked").
> 
> Yeah, that is an attitude not compatible with existing code. Much like
> the proposal to allow temporary/wide stores on everything not explicitly
> declared atomic. Such stuff instantly breaks all extant code that does
> multi-threading with no recourse.

If someone suggests temporary/wide stores, even on non-atomics, tell
them that the standard does not permit them to introduce data races.

							Thanx, Paul