From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757414Ab3KZQqH (ORCPT ); Tue, 26 Nov 2013 11:46:07 -0500 Received: from userp1040.oracle.com ([156.151.31.81]:29230 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757239Ab3KZQqD (ORCPT ); Tue, 26 Nov 2013 11:46:03 -0500 Date: Tue, 26 Nov 2013 11:45:52 -0500 From: Konrad Rzeszutek Wilk To: David Vrabel Cc: Ian.Campbell@citrix.com, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, JBeulich@suse.com, boris.ostrovsky@oracle.com Subject: Re: [PATCH 3/4] xen/manage: Guard against user-space initiated poweroff and XenBus. Message-ID: <20131126164552.GF2959@phenom.dumpdata.com> References: <1383932286-25080-1-git-send-email-konrad.wilk@oracle.com> <1383932286-25080-4-git-send-email-konrad.wilk@oracle.com> <528DEA00.7070505@citrix.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <528DEA00.7070505@citrix.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Source-IP: acsinet21.oracle.com [141.146.126.237] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 21, 2013 at 11:09:52AM +0000, David Vrabel wrote: > On 08/11/13 17:38, Konrad Rzeszutek Wilk wrote: > > There is a race case where the user does 'poweroff' > > and at the same time the system admin does 'xl shutdown'. > > This isn't a Xen-specific problem is it? Wouldn't it be better to fix > this in generic code? Possibly. I believe the reason for the reboot_notifier to exist is to provide a means to fix the race. > > Especially since I don't think this patch actually fixes the race > completely. > > > --- a/drivers/xen/manage.c > > +++ b/drivers/xen/manage.c > [...] > > @@ -222,7 +230,7 @@ static void shutdown_handler(struct xenbus_watch *watch, > > }; > > static struct shutdown_handler *handler; > > > > - if (shutting_down != SHUTDOWN_INVALID) > > + if (atomic_read(&shutting_down) != SHUTDOWN_INVALID) > > return; > > In guest initiated poweroff at this time will still race with this > toolstack initiated poweroff. No, b/c the reboot notifier would have set 'shutting_down' already. > > David