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=-17.5 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 D591BC433E0 for ; Mon, 8 Feb 2021 12:03:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9053364E60 for ; Mon, 8 Feb 2021 12:03:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233597AbhBHMDT (ORCPT ); Mon, 8 Feb 2021 07:03:19 -0500 Received: from mail.xenproject.org ([104.130.215.37]:50458 "EHLO mail.xenproject.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233295AbhBHLlR (ORCPT ); Mon, 8 Feb 2021 06:41:17 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=xen.org; s=20200302mail; h=Content-Transfer-Encoding:Content-Type:In-Reply-To: MIME-Version:Date:Message-ID:From:References:Cc:To:Subject; bh=zGrVRyh4Bb806FG6nBatBhxLklpw43eAz07n9qXefLM=; b=xB+0y4mG9nGyv+K0rMSe7assdJ Blahn0VgEg8Z2h3s3tSzkEDkVSLPk8YVcpox5SrzLQSMtLCND17pUY4746K1Rf/aCyLYeX05a6aBV LBMzMH6iJ7qhPg76qhe4KgSgnpBFn1GsWh29UzJj56x7WqovrDEFuHAPIWCJKjCGwgRQ=; Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1l94u2-0002aq-Ul; Mon, 08 Feb 2021 11:40:26 +0000 Received: from [54.239.6.177] (helo=a483e7b01a66.ant.amazon.com) by xenbits.xenproject.org with esmtpsa (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1l94u2-0000zS-Lb; Mon, 08 Feb 2021 11:40:26 +0000 Subject: Re: [PATCH 7/7] xen/evtchn: read producer index only once To: Juergen Gross , xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org Cc: Boris Ostrovsky , Stefano Stabellini References: <20210206104932.29064-1-jgross@suse.com> <20210206104932.29064-8-jgross@suse.com> From: Julien Grall Message-ID: <8032d8a9-b28f-95e1-a5a8-e955ada4dc0a@xen.org> Date: Mon, 8 Feb 2021 11:40:24 +0000 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <20210206104932.29064-8-jgross@suse.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/02/2021 10:49, Juergen Gross wrote: > In evtchn_read() use READ_ONCE() for reading the producer index in > order to avoid the compiler generating multiple accesses. > > Signed-off-by: Juergen Gross > --- > drivers/xen/evtchn.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/xen/evtchn.c b/drivers/xen/evtchn.c > index 421382c73d88..f6b199b597bf 100644 > --- a/drivers/xen/evtchn.c > +++ b/drivers/xen/evtchn.c > @@ -211,7 +211,7 @@ static ssize_t evtchn_read(struct file *file, char __user *buf, > goto unlock_out; > > c = u->ring_cons; > - p = u->ring_prod; > + p = READ_ONCE(u->ring_prod); For consistency, don't you also need the write side in evtchn_interrupt() to use WRITE_ONCE()? > if (c != p) > break; > > -- Julien Grall