linux-kernel - Re: tuntap regression in v3.9.8 and v3.10

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Date:	Wed, 3 Jul 2013 00:06:51 +0200
From:	Thomas Zeitlhofer <thomas.zeitlhofer@...tuwien.ac.at>
To:	Fabio Estevam <festevam@...il.com>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	jasowang@...hat.com
Subject: Re: tuntap regression in v3.9.8 and v3.10

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@...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).
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