From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755633Ab2GJPY2 (ORCPT ); Tue, 10 Jul 2012 11:24:28 -0400 Received: from mo-p00-ob.rzone.de ([81.169.146.162]:10757 "EHLO mo-p00-ob.rzone.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753607Ab2GJPY1 (ORCPT ); Tue, 10 Jul 2012 11:24:27 -0400 X-RZG-AUTH: :P2EQZWCpfu+qG7CngxMFH1J+zrwiavkK6tmQaLfmwtM48/lr387qFmLE X-RZG-CLASS-ID: mo00 Date: Tue, 10 Jul 2012 17:24:25 +0200 From: Olaf Hering To: Konrad Rzeszutek Wilk Cc: Jeremy Fitzhardinge , xen-devel@lists.xensource.com, linux-kernel@vger.kernel.org Subject: Re: [Xen-devel] [PATCH] xen/pv-on-hvm kexec: shutdown watches from old kernel Message-ID: <20120710152424.GB31819@aepfle.de> References: <1341924603-18978-1-git-send-email-olaf@aepfle.de> <20120710141906.GC1791@phenom.dumpdata.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20120710141906.GC1791@phenom.dumpdata.com> User-Agent: Mutt/1.5.21.rev5543 (2011-12-20) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 10, Konrad Rzeszutek Wilk wrote: > On Tue, Jul 10, 2012 at 02:50:03PM +0200, Olaf Hering wrote: > > Add xs_reset_watches function to shutdown watches from old kernel after > > kexec boot. The old kernel does not unregister all watches in the > > shutdown path. They are still active, the double registration can not > > be detected by the new kernel. When the watches fire, unexpected events > > will arrive and the xenwatch thread will crash (jumps to NULL). An > > orderly reboot of a hvm guest will destroy the entire guest with all its > > resources (including the watches) before it is rebuilt from scratch, so > > the missing unregister is not an issue in that case. > > > > With this change the xenstored is instructed to wipe all active watches > > for the guest. However, a patch for xenstored is required so that it > > accepts the XS_RESET_WATCHES request from a client (see changeset > > 23839:42a45baf037d in xen-unstable.hg). Without the patch for xenstored > > the registration of watches will fail and some features of a PVonHVM > > guest are not available. The guest is still able to boot, but repeated > > kexec boots will fail. > > OK, so this should make the reset of xenstore work with the new hypervisor, > but with older ones (like Amazon), it won't and we won't have regressions, right? The reset happens only if "platform-feature-xs_reset_watches" exists, so old hosts are supposed to be ok. Olaf