linux-kernel - Re: [PATCH] arm64: Implement 1-,2- byte smp_load_acquire and smp_store

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Message-ID: <CA+55aFwgG0pNwp3ywOsaEfeArD43MoJ9VLbUYQ8DCKN30=mLOA@mail.gmail.com>
Date:	Mon, 20 Apr 2015 09:08:37 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andrey Ryabinin <a.ryabinin@...sung.com>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: Implement 1-,2- byte smp_load_acquire and smp_store_release

On Mon, Apr 20, 2015 at 8:45 AM, Andrey Ryabinin <a.ryabinin@...sung.com> wrote:
>
> Commit 8053871d0f7f ("smp: Fix smp_call_function_single_async() locking")
> started to use smp_load_acquire() to load 2-bytes csd->flags.
> That crashes arm64 kernel during the boot.

Ahh. I don't disagree with your patch, but we should just make
csd->flags be an "int" regardless of this issue.

There is absolutely no reason to try to use 16-bit words. It doesn't
save us any space (alignment), and it's just a *bad* idea to depend on
any kind of atomicity of 16-bit entities. Bytes, yes. Words, yes. But
16-bit half-words? There's no point.

So I'll make it "unsigned int" instead of "u16".

But as said, the ARM64 patch definitely is a good idea regardless.

                          Linus
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