Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932856AbYCSUXj (ORCPT ); Wed, 19 Mar 2008 16:23:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757344AbYCSTj0 (ORCPT ); Wed, 19 Mar 2008 15:39:26 -0400 Received: from gw.goop.org ([64.81.55.164]:39425 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757222AbYCSTir (ORCPT ); Wed, 19 Mar 2008 15:38:47 -0400 Message-ID: <47DFE75B.7080404@goop.org> Date: Tue, 18 Mar 2008 09:01:31 -0700 From: Jeremy Fitzhardinge User-Agent: Thunderbird 2.0.0.12 (X11/20080226) MIME-Version: 1.0 To: "Christopher S. Aker" CC: Xen-devel , Linux Kernel Mailing List , virtualization@lists.linux-foundation.org, xming Subject: Re: [Xen-devel] Re: Xen paravirt frontend block hang References: <4772AC8E.7010007@theshore.net> <47C712EF.1060703@goop.org> <47C9F818.4020200@theshore.net> <47CAC931.1000107@goop.org> <47CACFBE.5010007@theshore.net> In-Reply-To: <47CACFBE.5010007@theshore.net> X-Enigmail-Version: 0.95.6 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1294 Lines: 27 Christopher S. Aker wrote: > Jeremy Fitzhardinge wrote: >> Are you running an SMP or UP domain? I found I could get hangs very >> easily with UP (but I need confirm it isn't a result of some other >> very experimental patches). > > The hang occurs with both SMP and UP compiled pv_ops kernels. SMP > kernels are still slightly responsive after the hang occurs, which > makes me think only one proc gets stuck at a time, not the entire kernel. The patch I posted yesterday - "xen: fix RMW when unmasking events" - should definitively fix the hanging-under-load bugs (I hope). It problem came from returning to userspace with pending events, which would leave them hanging around on the vcpu unprocessed, and eventually everything would deadlock. This was caused by using an unlocked read-modify-write operation on the event pending flag - which can be set by another (real) cpu - meaning that the pending event wasn't noticed until too late. It would only be a problem on an SMP host. The patch should back-apply to 2.6.24. J -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/