Re: tuntap regression in v3.9.8 and v3.10

[Thomas Zeitlhofer <thomas.zeitlhofer@nt.tuwien.ac.at>]

Hello Jason,

On Wed, Jul 03, 2013 at 10:44:32AM +0800, Jason Wang wrote:
> On 07/03/2013 06:06 AM, Thomas Zeitlhofer wrote:
> > On Tue, Jul 02, 2013 at 06:01:12PM -0300, Fabio Estevam wrote:
> >> On Tue, Jul 2, 2013 at 4:59 PM, Thomas Zeitlhofer
> >> <thomas.zeitlhofer@nt.tuwien.ac.at> wrote:
> >>> Commit "tuntap: set SOCK_ZEROCOPY flag during open" introduces a
> >>> regression which is observed with live migration of qemu/kvm based
> >>> virtual machines that are connected to an openvswitch bridge.
> >>>
> >>> Reverting this commit (b26c93c46a3dec25ed236d4ba6107eb4ed5d9401 in
> >>> v3.9.8 and accordingly 19a6afb23e5d323e1245baa4e62755492b2f1200 in
> >>> v3.10) fixes the following problem:
> >> Should the sock_set_flag stay in tun_set_iff as it was prior to 54f968d6efd?
> >>
> >> --- a/drivers/net/tun.c
> >> +++ b/drivers/net/tun.c
> >> @@ -1652,6 +1652,7 @@ static int tun_set_iff(struct net *net, struct
> >> file *file, struct ifreq *ifr)
> >>                 tun->txflt.count = 0;
> >>                 tun->vnet_hdr_sz = sizeof(struct virtio_net_hdr);
> >>
> >> +               sock_set_flag(&tfile->sk, SOCK_ZEROCOPY);
> >>                 tun->filter_attached = false;
> >>                 tun->sndbuf = tfile->socket.sk->sk_sndbuf;
> >>
> >> @@ -2159,8 +2160,6 @@ static int tun_chr_open(struct inode *inode,
> >> struct file * file)
> >>         set_bit(SOCK_EXTERNALLY_ALLOCATED, &tfile->socket.flags);
> >>         INIT_LIST_HEAD(&tfile->next);
> >>
> >> -       sock_set_flag(&tfile->sk, SOCK_ZEROCOPY);
> >> -
> >>         return 0;
> >>  }
> > I guess no, as this also leads to a kernel panic (tested against v3.10).
> 
> Yes, commit "tuntap: set SOCK_ZEROCOPY flag during open" just re-enable
> the zerocopy capability of tuntap. I believe it just uncover other
> zerocopy bugs.
> 
> Which regression did you see?

a kernel panic on the host machine. The details are in the first message
of this thread: http://lkml.org/lkml/2013/7/2/499