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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 D003DC2BA19 for ; Wed, 15 Apr 2020 12:29:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A019E20936 for ; Wed, 15 Apr 2020 12:29:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="UYHl/yOv" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2409914AbgDOM3G (ORCPT ); Wed, 15 Apr 2020 08:29:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41510 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2409123AbgDOLpE (ORCPT ); Wed, 15 Apr 2020 07:45:04 -0400 Received: from merlin.infradead.org (unknown [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 16A44C061A0C for ; Wed, 15 Apr 2020 04:45:04 -0700 (PDT) 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=F0TfwyL8cSoc6EbuwXOEHdNQToqkZSCb0ZeMj1NZt6Y=; b=UYHl/yOv/tYtFT7s05SpGr0Aep u9OV4QmhxJFMBHGAUrYs9WCxILLk/xtgHJcKEiySuB8o1WxrsdkSxCkUlcRNr5GGWx08t9HfDCWk5 FazvGzuDeGDbBm9dQxXRitKQugJmnIvbqyBeh9yADPznN71P4reB7nVPhd7YsxZ8ZM+5CU/TTd+9a cPQdthDc1qTYLZkcs0AzpN16uh9nVCkMLrqrRmT3P+i5El3nNFgK6LoChcXovkvOgwHPiIvZxyFon AmCPSXDSbgSj+S56//tUTQFMlsaqznAb74qvIAUqxlzznob8LFl3T1w7P5JBLeKbjBWVVIA8Y9f9B c7IYsvHQ==; 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 1jOgTD-0000yb-V3; Wed, 15 Apr 2020 11:44:44 +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 A0A8730066E; Wed, 15 Apr 2020 13:44:41 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 57FA12038BC5A; Wed, 15 Apr 2020 13:44:41 +0200 (CEST) Date: Wed, 15 Apr 2020 13:44:41 +0200 From: Peter Zijlstra To: Will Deacon Cc: Muchun Song , mingo@redhat.com, mingo@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] seqlock: Use while instead of if+goto in __read_seqcount_begin Message-ID: <20200415114441.GG20730@hirez.programming.kicks-ass.net> References: <20200409134558.90863-1-songmuchun@bytedance.com> <20200410115658.GB24814@willie-the-truck> <20200414110516.GO20713@hirez.programming.kicks-ass.net> <20200414134830.GB28750@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200414134830.GB28750@willie-the-truck> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 14, 2020 at 02:48:31PM +0100, Will Deacon wrote: > Oh yeah, good thinking. Didn't spot that one, but it should work well as > long as smp_cond_load_relaxed() always implies a control dependency (surely > it has to?) Well, yeah, but then you know as well as I do that compilers are dodgy pieces of crap which are out to get you. Still, I too can't see how it could mess this up.