From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751458AbaDAMxp (ORCPT ); Tue, 1 Apr 2014 08:53:45 -0400 Received: from smtp02.citrix.com ([66.165.176.63]:25978 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751247AbaDAMxo (ORCPT ); Tue, 1 Apr 2014 08:53:44 -0400 X-IronPort-AV: E=Sophos;i="4.97,772,1389744000"; d="scan'208";a="115670416" Message-ID: <533AB6D4.2050807@citrix.com> Date: Tue, 1 Apr 2014 13:53:40 +0100 From: David Vrabel User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.16) Gecko/20121215 Iceowl/1.0b1 Icedove/3.0.11 MIME-Version: 1.0 To: Konrad Rzeszutek Wilk CC: David Vrabel , , , , , Subject: Re: [Xen-devel] [PATCH 4/4] xen/xenbus: Avoid synchronous wait on XenBus stalling shutdown/restart. References: <1383932286-25080-1-git-send-email-konrad.wilk@oracle.com> <1383932286-25080-5-git-send-email-konrad.wilk@oracle.com> <528E485C.5030906@citrix.com> <20131126165016.GH2959@phenom.dumpdata.com> <529C7205.3060406@citrix.com> <20140331203313.GA6756@phenom.dumpdata.com> In-Reply-To: <20140331203313.GA6756@phenom.dumpdata.com> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.80.2.76] X-DLP: MIA1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 31/03/14 21:33, Konrad Rzeszutek Wilk wrote: > > Subject: [PATCH] xen/xenbus: Avoid synchronous wait on XenBus stalling > shutdown/restart. > > The 'read_reply' works with 'process_msg' to read of a reply in XenBus. > 'process_msg' is running from within the 'xenbus' thread. Whenever > a message shows up in XenBus it is put on a xs_state.reply_list list > and 'read_reply' picks it up. > > The problem is if the backend domain or the xenstored process is killed. > In which case 'xenbus' is still awaiting - and 'read_reply' if called - > stuck forever waiting for the reply_list to have some contents. > > This is normally not a problem - as the backend domain can come back > or the xenstored process can be restarted. However if the domain > is in process of being powered off/restarted/halted - there is no > point of waiting on it coming back - as we are effectively being > terminated and should not impede the progress. > > This patch solves this problem by checking whether the guest is > the right domain. If it is an initial domain and hurtling towards > death - there is no point of continuing the wait. All other type > of guests continue with their behavior. > mechanism a bit more asynchronous. Reviewed-by: David Vrabel David