linux-kernel - Re: [RFC][PATCH 0/5] arch: atomic rework

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Message-ID: <20140212181205.GD27965@twins.programming.kicks-ass.net>
Date:	Wed, 12 Feb 2014 19:12:05 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Torvald Riegel <triegel@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Will Deacon <will.deacon@....com>,
	Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
	David Howells <dhowells@...hat.com>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"gcc@....gnu.org" <gcc@....gnu.org>
Subject: Re: [RFC][PATCH 0/5] arch: atomic rework

On Wed, Feb 12, 2014 at 09:42:09AM -0800, Paul E. McKenney wrote:
> You need volatile semantics to force the compiler to ignore any proofs
> it might otherwise attempt to construct.  Hence all the ACCESS_ONCE()
> calls in my email to Torvald.  (Hopefully I translated your example
> reasonably.)

My brain gave out for today; but it did appear to have the right
structure.

I would prefer it C11 would not require the volatile casts. It should
simply _never_ speculate with atomic writes, volatile or not.



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