netdev - Re: Linux 4.14 - regression: broken tun/tap / bridge network with virtio

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Message-ID: <20171208114025.kjcaratqcveq7zu5@unicorn.suse.cz>
Date:   Fri, 8 Dec 2017 12:40:25 +0100
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Andreas Hartmann <andihartmann@...19freenet.de>
Cc:     Jason Wang <jasowang@...hat.com>,
        David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: Linux 4.14 - regression: broken tun/tap / bridge network with
 virtio - bisected

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.

> > If this is the case, you should try commit 0c19f846d582 ("net:
> > accept UFO datagrams from tuntap and packet"). 
> 
> It doesn't apply to 4.14.4
> 
> > Or disabling UFO in the guest should
> > work around the issue.
> 
> ethtool -K ethX ufo off for each device / bridge in VM.
> 
> Yes, this seems to work. I'll wait and see if the non stoppable
> qemu-problem on shutdown will remain.
> 
> When will there be a fix for 4.14? It is clearly a regression. Is it
> possible / a good idea to just remove the complete patch series "Remove
> UDP Fragmentation Offload support"?

I cannot give an exact date but the patch is queued for stable
(see http://patchwork.ozlabs.org/bundle/davem/stable/?state=* ) so that
it should land in stable-4.14 in near future (weeks at most).

                                                         Michal Kubecek