From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andreas Hartmann Subject: Re: Linux 4.14 - regression: broken tun/tap / bridge network with virtio - bisected Date: Fri, 8 Dec 2017 21:11:53 +0100 Message-ID: <96a16c1f-c026-f506-78c1-dad88471361d@01019freenet.de> References: <9615150a-eb78-2f9d-798f-6aa460932aec@01019freenet.de> <2e2392b7-84c5-be89-b0e5-5bae3b2fdaed@01019freenet.de> <4efbaf24-f419-2c8e-c705-59a5242b0575@01019freenet.de> <881560f8-54ec-e946-50cb-b2e80ddb5f97@01019freenet.de> <73b7a7b0-4264-2bd0-9e65-69841377f09f@redhat.com> <401a0715-fd28-63a3-8dfd-e89835d70db0@01019freenet.de> <11c25b88-af9b-a1f7-b5f5-0420c75916d7@01019freenet.de> <20171208084751.tom4auppogz4lanz@unicorn.suse.cz> <20171208114025.kjcaratqcveq7zu5@unicorn.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: Jason Wang , David Miller , Network Development To: Willem de Bruijn , Michal Kubecek Return-path: Received: from mx2.mailbox.org ([80.241.60.215]:38144 "EHLO mx2.mailbox.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753012AbdLHUMA (ORCPT ); Fri, 8 Dec 2017 15:12:00 -0500 In-Reply-To: Content-Language: en-US Sender: netdev-owner@vger.kernel.org List-ID: On 12/08/2017 at 05:04 PM Willem de Bruijn wrote: > On Fri, Dec 8, 2017 at 6:40 AM, Michal Kubecek wrote: >> On Fri, Dec 08, 2017 at 11:31:50AM +0100, Andreas Hartmann wrote: >>> On 12/08/2017 at 09:47 AM Michal Kubecek wrote: >>>> On Fri, Dec 08, 2017 at 08:21:16AM +0100, Andreas Hartmann wrote: >>>>> >>>>> All my VMs are using virtio_net. BTW: I couldn't see the problems >>>>> (sometimes, the VM couldn't be stopped at all) if all my VMs are using >>>>> e1000 as interface instead. >>>>> >>>>> This finding now matches pretty much the responsible UDP-package which >>>>> caused the stall. I already mentioned it here [2]. >>>>> >>>>> To prove it, I reverted from the patch series "[PATCH v2 RFC 0/13] >>>>> Remove UDP Fragmentation Offload support" [3] >>>>> >>>>> 11/13 [v2,RFC,11/13] net: Remove all references to SKB_GSO_UDP. [4] >>>>> 12/13 [v2,RFC,12/13] inet: Remove software UFO fragmenting code. [5] >>>>> 13/13 [v2,RFC,13/13] net: Kill NETIF_F_UFO and SKB_GSO_UDP. [6] >>>>> >>>>> and applied it to Linux 4.14.4. It compiled fine and is running fine. >>>>> The vnet doesn't die anymore. Yet, I can't say if the qemu stop hangs >>>>> are gone, too. >>>>> >>>>> Obviously, there is something broken with the new UDP handling. Could >>>>> you please analyze this problem? I could test some more patches ... . >>>> >>>> Any chance your VMs were live migrated from pre-4.14 host kernel? >>> >>> No - the VMs are not live migrated. They are always running on the same >>> host - either with kernel < 4.14 or with kernel 4.14.x. >> >> This is disturbing... unless I'm mistaken, it shouldn't be possible to >> have UFO enabled on a virtio device in a VM booted on a host with 4.14 >> kernel. > > Indeed. When working on that revert patch I verified that UFO in > the guest virtio_net was off before the revert patch, on after. > > Qemu should check host support with tap_probe_has_ufo > before advertising support to the guest. Indeed, this is exactly > what broke live migration in virtio_net_load_device at > > if (qemu_get_byte(f) && !peer_has_ufo(n)) { > error_report("virtio-net: saved image requires TUN_F_UFO support"); > return -1; > } > > Which follows > > peer_has_ufo > qemu_has_ufo > tap_has_ufo > s->has_ufo > > where s->has_ufo was set by tap_probe_has_ufo in net_tap_fd_init. > > Now, checking my qemu git branch, I ran pretty old 2.7.0-rc3. But this > codepath does not seem to have changed between then and 2.10.1. > > I cherry-picked the revert onto 4.14.3. It did not apply cleanly, but the > fix-up wasn't too hard. Compiled and booted, but untested otherwise. At > > https://github.com/wdebruij/linux/commits/v4.14.3-aargh-ufo I'm just running it at the moment. I didn't face any network hang until now - although the critical UDP packages have been gone through. Therefore: looks nice. Thanks, Andreas