Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752691AbaBRVr6 (ORCPT ); Tue, 18 Feb 2014 16:47:58 -0500 Received: from mx1.redhat.com ([209.132.183.28]:40153 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751982AbaBRVrz (ORCPT ); Tue, 18 Feb 2014 16:47:55 -0500 Subject: Re: [RFC][PATCH 0/5] arch: atomic rework From: Torvald Riegel To: Peter Zijlstra Cc: Linus Torvalds , Alec Teal , Paul McKenney , Will Deacon , Ramana Radhakrishnan , David Howells , "linux-arch@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "akpm@linux-foundation.org" , "mingo@kernel.org" , "gcc@gcc.gnu.org" In-Reply-To: <20140218214047.GU14089@laptop.programming.kicks-ass.net> References: <1392486310.18779.6447.camel@triegel.csb> <1392666947.18779.6838.camel@triegel.csb> <530296CD.5050503@warwick.ac.uk> <1392737465.18779.7644.camel@triegel.csb> <1392758516.18779.8378.camel@triegel.csb> <20140218214047.GU14089@laptop.programming.kicks-ass.net> Content-Type: text/plain; charset="UTF-8" Date: Tue, 18 Feb 2014 22:47:15 +0100 Message-ID: <1392760035.18779.8449.camel@triegel.csb> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2014-02-18 at 22:40 +0100, Peter Zijlstra wrote: > On Tue, Feb 18, 2014 at 10:21:56PM +0100, Torvald Riegel wrote: > > Well, that's how atomics that aren't volatile are defined in the > > standard. I can see that you want something else too, but that doesn't > > mean that the other thing is broken. > > Well that other thing depends on being able to see the entire program at > compile time. PaulMck already listed various ways in which this is > not feasible even for normal userspace code. > > In particular; DSOs and JITs were mentioned. No it doesn't depend on whole-program analysis being possible. Because if it isn't, then a correct compiler will just not do certain optimizations simply because it can't prove properties required for the optimization to hold. With the exception of access to objects via magic numbers (e.g., fixed and known addresses (see my reply to Paul), which are outside of the semantics specified in the standard), I don't see a correctness problem here. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/