linux-kernel - Re: linux-next: build warnings after merge of the access

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Message-ID: <CA+55aFw6f4sLc4DMTmd2T9-r8NNQq8Zr4Wf1SvHSG=s1Vd-WuA@mail.gmail.com>
Date:	Thu, 26 Mar 2015 10:52:02 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Christian Borntraeger <borntraeger@...ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Will Deacon <will.deacon@....com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	"linux-next@...r.kernel.org" <linux-next@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>
Subject: Re: linux-next: build warnings after merge of the access_once tree

On Thu, Mar 26, 2015 at 10:24 AM, Christian Borntraeger
<borntraeger@...ibm.com> wrote:
>
> Oh I just added that check back then because some guy named
> Linus suggested something like that ;-)

Yes, my bad.

In my defense, that was when we were talking about ACCESS_ONCE()
causing bugs with gcc due to the blind use of "volatile" that it turns
out gcc doesn't necessarily like.

With the memcpy fallback (and the simpler "scalar pointer copy by
hand"), I think READ_ONCE() (and WRITE_ONCE()) are safe.

                      Linus
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