From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=FAKE_REPLY_C, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9AED6C433EF for ; Mon, 9 Sep 2019 06:22:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 770EE20828 for ; Mon, 9 Sep 2019 06:22:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727878AbfIIGWQ (ORCPT ); Mon, 9 Sep 2019 02:22:16 -0400 Received: from helcar.hmeau.com ([216.24.177.18]:32804 "EHLO fornost.hmeau.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728039AbfIIGWP (ORCPT ); Mon, 9 Sep 2019 02:22:15 -0400 Received: from gwarestrin.arnor.me.apana.org.au ([192.168.0.7]) by fornost.hmeau.com with smtp (Exim 4.89 #2 (Debian)) id 1i7D3C-0006NS-Ao; Mon, 09 Sep 2019 16:21:23 +1000 Received: by gwarestrin.arnor.me.apana.org.au (sSMTP sendmail emulation); Mon, 09 Sep 2019 16:21:11 +1000 Date: Mon, 9 Sep 2019 16:21:11 +1000 From: Herbert Xu To: Peter Zijlstra Cc: torvalds@linux-foundation.org, mathieu.desnoyers@efficios.com, tglx@linutronix.de, joel@joelfernandes.org, stern@rowland.harvard.edu, rostedt@goodmis.org, valentin.schneider@arm.com, linux-kernel@vger.kernel.org, paulmck@linux.ibm.com, boqun.feng@gmail.com, will.deacon@arm.com, dhowells@redhat.com Subject: Re: [PATCH 1/1] Fix: trace sched switch start/stop racy updates Message-ID: <20190909062111.GA14572@gondor.apana.org.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190820135612.GS2332@hirez.programming.kicks-ass.net> X-Newsgroups: apana.lists.os.linux.kernel User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Peter Zijlstra wrote: > > Paulmck actually has an example of that somewhere; ISTR that particular > case actually got fixed by GCC, but I'd really _love_ for some compiler > people (both GCC and LLVM) to state that their respective compilers will > not do load/store tearing for machine word sized load/stores. > > Without this written guarantee (which supposedly was in older GCC > manuals but has since gone missing), I'm loathe to rely on it. IIRC in that case gcc actually broke atomic writes even with a volatile keyword. So even WRITE_ONCE wouldn't have saved us. Cheers, -- Email: Herbert Xu Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt