From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 18/18] arm64: lto: Strengthen READ_ONCE() to acquire when
 CLANG_LTO=y
Date: Tue, 30 Jun 2020 22:20:59 +0200
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To: Marco Elver <elver@google.com>
Cc: Will Deacon <will@kernel.org>, LKML <linux-kernel@vger.kernel.org>, Sami Tolvanen <samitolvanen@google.com>, Nick Desaulniers <ndesaulniers@google.com>, Kees Cook <keescook@chromium.org>, "Paul E. McKenney" <paulmck@kernel.org>, Josh Triplett <josh@joshtriplett.org>, Matt Turner <mattst88@gmail.com>, Ivan Kokshaysky <ink@jurassic.park.msu.ru>, Richard Henderson <rth@twiddle.net>, Alan Stern <stern@rowland.harvard.edu>, "Michael S. Tsirkin" <mst@redhat.com>, Jason Wang <jasowang@redhat.com>, Arnd Bergmann <arnd@arndb.de>, Boqun Feng <boqun.feng@gmail.com>, Catalin Marinas <catalin.marinas@arm.com>, Mark Rutland <mark.rutland@arm.com>, linux-arm-kernel@lists.infradead.org, linux-alpha@vger.kernel.org, virtualization@lists.linux-foundation.org
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On Tue, Jun 30, 2020 at 09:47:30PM +0200, Marco Elver wrote:
> I do wonder, though, if there is some way to make the compiler do
> something better for us. Clearly, implementing real
> memory_order_consume hasn't worked out until today. But maybe the
> compiler could promote dependent loads to acquires if it recognizes it
> lost dependencies during optimizations. Just thinking out loud, it
> probably still has some weird corner case that will break. ;-)

I'd be very hesitant to let the compiler upgrade the ordering for us,
specifically because we're not using C11 crud and are using a lot of
inline asm.