linux-kernel - Re: [PATCH/RFC 7/7] kernel: Force ACCESS

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Message-ID: <CA+55aFwJEqMv00zkwHmp_LOg74RU3e30-oo6RaYb=yGjgGr2cg@mail.gmail.com>
Date:	Mon, 24 Nov 2014 12:19:11 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Paul McKenney <paulmck@...ux.vnet.ibm.com>
Cc:	Christian Borntraeger <borntraeger@...ibm.com>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	David Howells <dhowells@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	linux-mips <linux-mips@...ux-mips.org>,
	linux-x86_64@...r.kernel.org,
	linux-s390 <linux-s390@...r.kernel.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>
Subject: Re: [PATCH/RFC 7/7] kernel: Force ACCESS_ONCE to work only on scalar types

On Mon, Nov 24, 2014 at 11:42 AM, Paul E. McKenney
<paulmck@...ux.vnet.ibm.com> wrote:
>
> OK, how about the following?

Ugh. Disgusting.

Why the heck isn't it just "sizeof(*__vp) <= sizeof(long)"?

If the architecture has a 3-byte scalar type, then it probably has a
3-byte load.

> It complains if the variable is too large, for example, long long on
> 32-bit systems or large structures.  It is OK loading from and storing
> to small structures as well, which I am having a hard time thinking of
> as a disadvantage.

.. but that's *exactly* the gcc bug in question. It's a word-sized
struct that gcc loads twice.

                          Linus
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