From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754979Ab3KURwc (ORCPT ); Thu, 21 Nov 2013 12:52:32 -0500 Received: from smtp02.citrix.com ([66.165.176.63]:44870 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753936Ab3KURwb (ORCPT ); Thu, 21 Nov 2013 12:52:31 -0500 X-IronPort-AV: E=Sophos;i="4.93,746,1378857600"; d="scan'208";a="74452635" Message-ID: <528E485C.5030906@citrix.com> Date: Thu, 21 Nov 2013 17:52:28 +0000 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: , , , , , 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> In-Reply-To: <1383932286-25080-5-git-send-email-konrad.wilk@oracle.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 08/11/13 17:38, Konrad Rzeszutek Wilk wrote: > 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 the 'system_state' value > to see if we are in heading towards death. We also make the wait > mechanism a bit more asynchronous. This seems to be checking the wrong thing conceptually. We should abort the wait if xenstored is dead not if our domain is dying. I think you can consider xenstored as dead if: a) it's local and we're dying. b) it's remote and the remote domain is dead. > Fixes-Bug: http://bugs.xenproject.org/xen/bug/8 This bug link has no useful information in it. > --- a/drivers/xen/xenbus/xenbus_xs.c > +++ b/drivers/xen/xenbus/xenbus_xs.c > @@ -148,9 +148,24 @@ static void *read_reply(enum xsd_sockmsg_type *type, unsigned int *len) > > while (list_empty(&xs_state.reply_list)) { > spin_unlock(&xs_state.reply_lock); > - /* XXX FIXME: Avoid synchronous wait for response here. */ > - wait_event(xs_state.reply_waitq, > - !list_empty(&xs_state.reply_list)); > + wait_event_timeout(xs_state.reply_waitq, > + !list_empty(&xs_state.reply_list), > + msecs_to_jiffies(500)); This is still a synchronous wait. Is the removal of the FIXME comment correct? > + > + /* > + * If we are in the process of being shut-down there is > + * no point of trying to contact XenBus - it is either > + * killed (xenstored application) or the other domain > + * has been killed or is unreachable. Not necessarily, xenstore could just be slow. David