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=-15.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 52559C433DB for ; Wed, 17 Feb 2021 13:32:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0EB7D64E5F for ; Wed, 17 Feb 2021 13:32:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232969AbhBQNcA (ORCPT ); Wed, 17 Feb 2021 08:32:00 -0500 Received: from esa1.hc3370-68.iphmx.com ([216.71.145.142]:17818 "EHLO esa1.hc3370-68.iphmx.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233015AbhBQNaV (ORCPT ); Wed, 17 Feb 2021 08:30:21 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=citrix.com; s=securemail; t=1613568621; h=subject:to:cc:references:from:message-id:date: mime-version:in-reply-to:content-transfer-encoding; bh=bp3fBtBumnQYDuMT4p4O4vegfrz8kk/nF90ppoE+EIQ=; b=LD8wHbTgeEH8lvrxKWZgn0dWL5OoUb7HGoRuBhlG4gR8rkT2miZHCG0N bIgGa/k8QFFzuqyJ6TU4XuVoPCpuiK2uUn6zTHpB82umeX5QpJgUqBBWx PQ6/ugS2Yo+Z1U57HJU9Y5ctocjGgNidEy3XJ2+vUdP5ALnwO1RL9jQ+0 g=; Authentication-Results: esa1.hc3370-68.iphmx.com; dkim=none (message not signed) header.i=none IronPort-SDR: o7LaJcbQT5QuBw1xPwkFm1kmmIpHK9sbb9lZj5IyJs4mA6AKdPwwmE6rjsZVBkmNqq+f1rg7v9 LhPjd42AWS+GmnJwjqQu2oMcrOsirvyJVxH5cCnpbZzFpjLStPB9qB5/CJH5wL2kyX3hIiHH41 BiJdvO1WYeF49G5IAxgFWe2Doce5WdQcFnPhB0gMWpqLGNUyZ04XS+fO43Jds6xWB/x8VdXjLc TVqBAY/waBGvsB5Nt+Gp+8G4G7JcUyHaEeserRUmk28EhENWIwM7fRM4ds93N++2/jeX9TnB7a ItU= X-SBRS: 5.1 X-MesageID: 37785213 X-Ironport-Server: esa1.hc3370-68.iphmx.com X-Remote-IP: 162.221.158.21 X-Policy: $RELAYED X-IronPort-AV: E=Sophos;i="5.81,184,1610427600"; d="scan'208";a="37785213" Subject: Re: [PATCH v2 8/8] xen/evtchn: use READ/WRITE_ONCE() for accessing ring indices To: Juergen Gross , , CC: Boris Ostrovsky , Stefano Stabellini References: <20210211101616.13788-1-jgross@suse.com> <20210211101616.13788-9-jgross@suse.com> From: Ross Lagerwall Message-ID: <6818fcde-abab-1250-119c-d0ccb8c80488@citrix.com> Date: Wed, 17 Feb 2021 13:29:19 +0000 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <20210211101616.13788-9-jgross@suse.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021-02-11 10:16, Juergen Gross wrote: > For avoiding read- and write-tearing by the compiler use READ_ONCE() > and WRITE_ONCE() for accessing the ring indices in evtchn.c. > > Signed-off-by: Juergen Gross > --- > V2: > - modify all accesses (Julien Grall) > --- > drivers/xen/evtchn.c | 25 ++++++++++++++++--------- > 1 file changed, 16 insertions(+), 9 deletions(-) > > diff --git a/drivers/xen/evtchn.c b/drivers/xen/evtchn.c > index 421382c73d88..620008f89dbe 100644 > --- a/drivers/xen/evtchn.c > +++ b/drivers/xen/evtchn.c > @@ -162,6 +162,7 @@ static irqreturn_t evtchn_interrupt(int irq, void *data) > { > struct user_evtchn *evtchn = data; > struct per_user_data *u = evtchn->user; > + unsigned int prod, cons; > > WARN(!evtchn->enabled, > "Interrupt for port %u, but apparently not enabled; per-user %p\n", > @@ -171,10 +172,14 @@ static irqreturn_t evtchn_interrupt(int irq, void *data) > > spin_lock(&u->ring_prod_lock); > > - if ((u->ring_prod - u->ring_cons) < u->ring_size) { > - *evtchn_ring_entry(u, u->ring_prod) = evtchn->port; > + prod = READ_ONCE(u->ring_prod); > + cons = READ_ONCE(u->ring_cons); > + > + if ((prod - cons) < u->ring_size) { > + *evtchn_ring_entry(u, prod) = evtchn->port; > smp_wmb(); /* Ensure ring contents visible */ > - if (u->ring_cons == u->ring_prod++) { > + if (cons == prod++) { > + WRITE_ONCE(u->ring_prod, prod); > wake_up_interruptible(&u->evtchn_wait); > kill_fasync(&u->evtchn_async_queue, > SIGIO, POLL_IN); This doesn't work correctly since now u->ring_prod is only updated if cons == prod++. Ross