Dave Jones davej@codemonkey.org.uk 于2019年8月13日周二 上午1:05写道：

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@scaleway.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

Small packets going out of a tap device go through an optimized code
path that uses build_skb() rather than sock_alloc_send_pskb(). The
latter calls skb_set_owner_w(), but the small packet code path does not.

The net effect is that small packets are not owned by the userland
application's socket (e.g. QEMU), while large packets are.
This can be seen with a TCP session, where packets are not owned when
the window size is small enough (around PAGE_SIZE), while they are once
the window grows (note that this requires the host to support virtio
tso for the guest to offload segmentation).
All this leads to inconsistent behaviour in the kernel, especially on
netfilter modules that uses sk->socket (e.g. xt_owner).

Fixes: 66ccbc9c87c2 ("tap: use build_skb() for small packet")
Signed-off-by: Alexis Bauvin <abauvin@scaleway.com>
Acked-by: Jason Wang <jasowang@redhat.com>

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.

    Dave

Thanks for reporting, Dave.

+cc stable Just noticed, the patch has been backported to 4.14,4.19, 5.2

Regards, Jack Wang