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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 6863BC83013 for ; Tue, 1 Dec 2020 18:56:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0337A20643 for ; Tue, 1 Dec 2020 18:56:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="0KTLGIr+" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731156AbgLAS4o (ORCPT ); Tue, 1 Dec 2020 13:56:44 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59426 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726213AbgLAS4n (ORCPT ); Tue, 1 Dec 2020 13:56:43 -0500 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 55F42C0613D4 for ; Tue, 1 Dec 2020 10:56:03 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=dP2aCGWV/QSuw3IqWekjEcVu6Gni8QIpKfoVcyJye9g=; b=0KTLGIr+J0voSyZKVgGtj/P7CP tTiyqemcQV5lMmwn/kvNMH97gkEv8jO2dxJyX3u1AHDXqkwuW0ksbtGmQkZvemfakBXQnEVMkEcJM idKQeRsgEtkrfLbm5wa+qzVJ6JM436Rmwqkv06+XBm0PlHpHzgSHKFoOtOikyq2EMPcG6O0cjb4wA fTxDzULqFRFKfFd/HWL1VarYB8jGTdqES09e213+o6zH83N7L2U5gtzANdPL64+97KYuL6XzFTDTz mUnx8Bgbh5PlueuZVqq7+wTf49z0NrJlRuzPRymhoo53ncvN41LK4oFbQ61FmnPVo4maw+oae0n8g ISzYb6hg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kkAog-0000dn-I9; Tue, 01 Dec 2020 18:55:58 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id F2E2D30018A; Tue, 1 Dec 2020 19:55:56 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id DDF3E2BF16C04; Tue, 1 Dec 2020 19:55:56 +0100 (CET) Date: Tue, 1 Dec 2020 19:55:56 +0100 From: Peter Zijlstra To: Andy Lutomirski Cc: X86 ML , Mathieu Desnoyers , LKML , Nicholas Piggin , Arnd Bergmann , Anton Blanchard Subject: Re: [PATCH 3/3] membarrier: Propagate SYNC_CORE and RSEQ actions more carefully Message-ID: <20201201185556.GV3040@hirez.programming.kicks-ass.net> References: <5495e4c344dc09011ff57756c7e0a1330830eafc.1606758530.git.luto@kernel.org> <20201201101637.GU2414@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 01, 2020 at 10:09:22AM -0800, Andy Lutomirski wrote: > > smp_call_function_single(.wait=1) already orders against completion of > > the IPI. Do we really need more? > > What kind of order does it provide? A quick skim of the code suggests > that it's an acquire barrier, but I think we need a full sequential > consistency barrier, at least on sufficiently weakly ordered > architectures. On x86, loads are ordered and this is probably > irrelevant. Also, this barrier was already there (it's the one I > deleted below), and I think that removing it should be its own patch > if we want to go that route. smp_mb() raise-IPI ----> /* do crud */ STORE-RELEASE csd->lock, 0; lock