From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754473AbbCLXgG (ORCPT ); Thu, 12 Mar 2015 19:36:06 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55177 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754011AbbCLXgB (ORCPT ); Thu, 12 Mar 2015 19:36:01 -0400 Date: Fri, 13 Mar 2015 07:35:52 +0800 From: Fam Zheng To: "Michael S. Tsirkin" Cc: linux-kernel@vger.kernel.org, Rusty Russell , virtualization@lists.linux-foundation.org, Paolo Bonzini , Jason Wang Subject: Re: [PATCH] virtio: Remove virtio device during shutdown Message-ID: <20150312233552.GB32054@ad.nay.redhat.com> References: <1426061357-4440-1-git-send-email-famz@redhat.com> <20150311095814-mutt-send-email-mst@redhat.com> <20150311101135.GA13653@ad.nay.redhat.com> <20150312172138-mutt-send-email-mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150312172138-mutt-send-email-mst@redhat.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 03/12 17:22, Michael S. Tsirkin wrote: > On Wed, Mar 11, 2015 at 06:11:35PM +0800, Fam Zheng wrote: > > On Wed, 03/11 10:06, Michael S. Tsirkin wrote: > > > On Wed, Mar 11, 2015 at 04:09:17PM +0800, Fam Zheng wrote: > > > > Currently shutdown is nop for virtio devices, but the core code could > > > > remove things behind us such as MSI-X handler etc. For example in the > > > > case of virtio-scsi-pci, the device may still try to send interupts, > > > > which will be on IRQ lines seeing MSI-X disabled. Those interrupts will > > > > be unhandled, and may cause flood. > > > > Here is the problem I want to solve - file system driver hang: > > > > If a fs code happen to hit __wait_on_buffer right after pci pci_device_shutdown > > disabled msix, it will never make progress because the requests it waits for > > will never be completed. So the system hangs. > > Paolo says that pci reset of virtio scsi device guarantees > that all outstanding requests complete. > > If true and implemented correctly, I don't see what else > needs to be done. > > You will need to debug this some more. First of all I was wrong about the fs driver above, scratch that, I'm sorry for the misleading. Regarding the hang in shutdown, Ulrich Obergfell has already pointed out that the vcpu is "busy/stuck in interrupt processing": https://bugzilla.redhat.com/attachment.cgi?id=998391 (RHBZ 1199155) Summary: The reason it is stuck is that an IRQ from virtio-scsi-pci is not handled. Why is there that IRQ? Because pci core code disabled msix. Why is it not handled? Because it's done behind virtio-scsi, who still is waiting for msix. "Hence, the interrupt will not be acknowledged and the guest becomes flooded with IRQ 11 interrupt." Fortunately it's not a livelock for upstream, because of: commit 184564efae4d775225c8fe3b762a56956fb1f827 Author: Zhang Haoyu Date: Thu Sep 11 16:47:04 2014 +0800 kvm: ioapic: conditionally delay irq delivery duringeoi broadcast But we still should do the shutdown right. I also propose to not shutdown msix from pci core shutdown if the device doesn't have shutdown function: http://www.spinics.net/lists/kernel/msg1944041.html With that patch is applied, the "nop" .shutdown in virtio-pci shouldn't hurt much. Regarding handing the requests, now I don't know if we really care about them at shutdown. As you said, waiting for requests may cause more hang. Ideas? Fam