netdev - Re: tun: mark small packets as owned by the tap sock

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Date:   Thu, 15 Aug 2019 13:11:39 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Dave Jones <davej@...emonkey.org.uk>
Cc:     Alexis Bauvin <abauvin@...leway.com>, netdev@...r.kernel.org
Subject: Re: tun: mark small packets as owned by the tap sock


On 2019/8/13 下午10:00, Dave Jones wrote:
> On Tue, Aug 13, 2019 at 04:33:59PM +0800, Jason Wang wrote:
>   >
>   > On 2019/8/13 上午6:19, Dave Jones wrote:
>   > > On Wed, Aug 07, 2019 at 12:30:07AM +0000, Linux Kernel wrote:
>   > >   > Commit:     4b663366246be1d1d4b1b8b01245b2e88ad9e706
>   > >   > Parent:     16b2084a8afa1432d14ba72b7c97d7908e178178
>   > >   > Web:        https://git.kernel.org/torvalds/c/4b663366246be1d1d4b1b8b01245b2e88ad9e706
>   > >   > Author:     Alexis Bauvin <abauvin@...leway.com>
>   > >   > AuthorDate: Tue Jul 23 16:23:01 2019 +0200
>   > >   >
>   > >   >     tun: mark small packets as owned by the tap sock
>   > >   >
>   > >   >     - v1 -> v2: Move skb_set_owner_w to __tun_build_skb to reduce patch size
>   > >
>   > > This commit breaks ipv6 routing when I deployed on it a linode.
>   > > It seems to work briefly after boot, and then silently all packets get
>   > > dropped. (Presumably, it's dropping RA or ND packets)
>   > >
>   > > With this reverted, everything works as it did in rc3.
>   > >
>   > Two questions:
>   >
>   > - Are you using XDP for TUN?
>
> not knowingly.
> $ grep XDP .config
> # CONFIG_XDP_SOCKETS is not set
>
> What's configured on the hypervisor side I have no idea.


Ok, please tell me more about your setups:

- Are you using TUN in host or guest?

- Are you using it for VM or VPN(tunneling)?

- Where did the packet get dropped?


>
>   > - Does it work before 66ccbc9c87c2?
>
> that's been around since 4.14-rc1, and at one point it ran whatever was
> in debian9 (4.9).  I don't recall it ever not working, so I'd say yes.
>
> I can build a 4.13 if it'll prove something, but it'll take me a while.
> (This is my primary MX, so it's dropping email while it's on the broken
>   kernel, so I need to plan some time to be around to babysit it)


If possible please try that.


>
>   > If yes, could you show us the result of net_dropmonitor?
>
> where do I get that?  It doesn't seem packaged for debian.
>
> 	Dave


It's part of perf-script(1). You can simply start it through perf script 
record net_dropmonitor.

Thanks

>