netdev - Re: [PATCH v2 net] ip6_gre: use skb_vlan_inet_prepare() instead of pskb_inet_may

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Message-ID: <CANn89i+95R86QaE=o4MxZSKr6ju3f44npMa7B27fgTGkVf6Z5w@mail.gmail.com>
Date: Mon, 12 Jan 2026 16:24:56 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Simon Horman <horms@...nel.org>
Cc: Florian Westphal <fw@...len.de>, Jakub Kicinski <kuba@...nel.org>, 
	"David S . Miller" <davem@...emloft.net>, Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com, syzbot+6023ea32e206eef7920a@...kaller.appspotmail.com, 
	Mazin Al Haddad <mazin@...state.dev>
Subject: Re: [PATCH v2 net] ip6_gre: use skb_vlan_inet_prepare() instead of pskb_inet_may_pull()

On Mon, Jan 12, 2026 at 2:58 PM Simon Horman <horms@...nel.org> wrote:
>
> On Wed, Jan 07, 2026 at 10:01:22AM +0100, Eric Dumazet wrote:
> > On Wed, Jan 7, 2026 at 9:46 AM Florian Westphal <fw@...len.de> wrote:
> > >
> > > Eric Dumazet <edumazet@...gle.com> wrote:
> > > > On Tue, Jan 6, 2026 at 6:56 PM Jakub Kicinski <kuba@...nel.org> wrote:
> > > > >
> > > > > On Tue,  6 Jan 2026 14:45:29 +0000 Eric Dumazet wrote:
> > > > > > v2: invert the conditions (Jakub)
> > > > >
> > > > > Thanks! Much better now, but still failing
> > > > > tools/testing/selftests/net/gre_gso.sh
> > > > >
> > > > > TAP version 13
> > > > > 1..1
> > > > > # timeout set to 3600
> > > > > # selftests: net: gre_gso.sh
> > > > > # 2.16 [+2.16]     TEST: GREv6/v4 - copy file w/ TSO                                   [ OK ]
> > > > > # 3.16 [+1.01] 2026/01/06 10:32:57 socat[20546] W exiting on signal 15
> > > > > # 3.17 [+0.01] 2026/01/06 10:32:57 socat[20546] W exiting on signal 15
> > > > > # 3.17 [+0.00]     TEST: GREv6/v4 - copy file w/ GSO                                   [FAIL]
> > > > > # 3.18 [+0.01] 2026/01/06 10:32:57 socat[20533] W exiting on signal 15
> > > > > # 3.19 [+0.00]     TEST: GREv6/v6 - copy file w/ TSO                                   [ OK ]
> > > > > # 4.19 [+1.00] 2026/01/06 10:32:59 socat[20559] W exiting on signal 15
> > > > > # 4.19 [+0.01]     TEST: GREv6/v6 - copy file w/ GSO                                   [FAIL]
> > > > > # 4.20 [+0.01] 2026/01/06 10:32:59 socat[20549] W exiting on signal 15
> > > > > # 4.22 [+0.02] 2026/01/06 10:32:59 socat[20560] W exiting on signal 15
> > > > > # 4.23 [+0.01]
> > > > > # 4.23 [+0.00] Tests passed:   2
> > > > > # 4.23 [+0.00] Tests failed:   2
> > > > > not ok 1 selftests: net: gre_gso.sh # exit=1
> > > > >
> > > > > https://netdev-ctrl.bots.linux.dev/logs/vmksft/net/results/461862/65-gre-gso-sh/stdout
> > > >
> > > > For some reason I am unable to run this test from a virtme-ng instance.
> > > >
> > > > I guess I wlll not make a new version of this patch, maybe Florian can
> > > > take over.
> > >
> > > Its failing because nhoff is moved by 14 bytes, test passes after doing:
> > >
> > > -       if (skb_vlan_inet_prepare(skb, false))
> > > +       if (skb_vlan_inet_prepare(skb, true))
> >
> > Thanks Florian.
> >
> > I finally understood that my virtme-ng problem with this test is that
> > on my platform, /proc/sys/net/core/fb_tunnels_only_for_init_net was
> > set to 2
> >
> > Tests have a hidden dependency against this sysctl.
>
> Should unhide it by making the tests check or set this value?
>
> It seems like a lot of time was lost on this already.

Or we could change iproute2 to no longer rely on the default devices.

2029  execve("/bin/ip", ["ip", "tunnel", "add", "gre1", "mode",
"ip6gre", "local", "fe80::782c:82ff:fe5d:68cc", "remote",
"fe80::8827:efff:feaf:1d87", "dev", "veth0"], 0x56329212d6e0 /* 12
vars */) = 0
2029  setsockopt(4, SOL_NETLINK, NETLINK_EXT_ACK, [1], 4) = 0
2029  bind(4, {sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, 12) = 0
2029  getsockname(4, {sa_family=AF_NETLINK, nl_pid=-2025971371,
nl_groups=00000000}, [12]) = 0
2029  sendmsg(4, {msg_name={sa_family=AF_NETLINK, nl_pid=0,
nl_groups=00000000}, msg_namelen=12,
msg_iov=[{iov_base=[{nlmsg_len=52, nlmsg_type=RTM_GETLINK,
nlmsg_flags=NLM_F_REQUEST, nlmsg_seq=1768231049, nlmsg_pid=0},
{ifi_family=AF_UNSPEC, ifi_type=ARPHRD_NETROM, ifi_index=0,
ifi_flags=0, ifi_change=0}, [[{nla_len=8, nla_type=IFLA_EXT_MASK},
RTEXT_FILTER_VF|RTEXT_FILTER_SKIP_STATS], [{nla_len=10,
nla_type=IFLA_IFNAME}, "veth0"]]], iov_len=52}], msg_iovlen=1,
msg_controllen=0, msg_flags=0}, 0) = 52
2029  recvmsg(4, {msg_name={sa_family=AF_NETLINK, nl_pid=0,
nl_groups=00000000}, msg_namelen=12, msg_iov=[{iov_base=NULL,
iov_len=0}], msg_iovlen=1, msg_controllen=0, msg_flags=MSG_TRUNC},
MSG_PEEK|MSG_TRUNC) = 832
2029  recvmsg(4, {msg_name={sa_family=AF_NETLINK, nl_pid=0,
nl_groups=00000000}, msg_namelen=12,
msg_iov=[{iov_base=[{nlmsg_len=832, nlmsg_type=RTM_NEWLINK,
nlmsg_flags=0, nlmsg_seq=1768231049, nlmsg_pid=-2025971371},
{ifi_family=AF_UNSPEC, ifi_type=ARPHRD_ETHER,
ifi_index=if_nametoindex("veth0"),
ifi_flags=IFF_UP|IFF_BROADCAST|IFF_RUNNING|IFF_MULTICAST|IFF_LOWER_UP,
ifi_change=0}, [[{nla_len=10, nla_type=IFLA_IFNAME}, "veth0"],
[{nla_len=8, nla_type=IFLA_TXQLEN}, 1000], [{nla_len=5,
nla_type=IFLA_OPERSTATE}, 6], [{nla_len=5, nla_type=IFLA_LINKMODE},
0], [{nla_len=5, nla_type=IFLA_NETNS_IMMUTABLE}, 0], [{nla_len=8,
nla_type=IFLA_MTU}, 1500], [{nla_len=8, nla_type=IFLA_MIN_MTU}, 68],
[{nla_len=8, nla_type=IFLA_MAX_MTU}, 65535], [{nla_len=8,
nla_type=IFLA_GROUP}, 0], [{nla_len=8, nla_type=IFLA_PROMISCUITY}, 0],
[{nla_len=8, nla_type=IFLA_ALLMULTI}, 0], [{nla_len=8,
nla_type=IFLA_NUM_TX_QUEUES}, 8], [{nla_len=8,
nla_type=IFLA_GSO_MAX_SEGS}, 65535], [{nla_len=8,
nla_type=IFLA_GSO_MAX_SIZE}, 65536], [{nla_len=8,
nla_type=IFLA_GRO_MAX_SIZE}, 65536], [{nla_len=8,
nla_type=IFLA_GSO_IPV4_MAX_SIZE}, 65536], [{nla_len=8,
nla_type=IFLA_GRO_IPV4_MAX_SIZE}, 65536], [{nla_len=8,
nla_type=IFLA_TSO_MAX_SIZE}, 524280], [{nla_len=8,
nla_type=IFLA_TSO_MAX_SEGS}, 65535], [{nla_len=8,
nla_type=IFLA_MAX_PACING_OFFLOAD_HORIZON}, "\x00\x00\x00\x00"],
[{nla_len=8, nla_type=IFLA_NUM_RX_QUEUES}, 8], [{nla_len=5,
nla_type=IFLA_CARRIER}, 1], [{nla_len=8,
nla_type=IFLA_CARRIER_CHANGES}, 2], [{nla_len=8,
nla_type=IFLA_CARRIER_UP_COUNT}, 1], [{nla_len=8,
nla_type=IFLA_CARRIER_DOWN_COUNT}, 1], [{nla_len=6, nla_type=0x44 /*
IFLA_??? */}, "\x00\x00"], [{nla_len=6, nla_type=0x45 /* IFLA_??? */},
"\x00\x00"], [{nla_len=5, nla_type=IFLA_PROTO_DOWN}, 0], [{nla_len=10,
nla_type=IFLA_ADDRESS}, 16:ad:38:9c:d2:4b], [{nla_len=10,
nla_type=IFLA_BROADCAST}, ff:ff:ff:ff:ff:ff], [{nla_len=12,
nla_type=IFLA_XDP}, [{nla_len=5, nla_type=IFLA_XDP_ATTACHED},
XDP_ATTACHED_NONE]], [{nla_len=16, nla_type=IFLA_LINKINFO},
[{nla_len=9, nla_type=IFLA_INFO_KIND}, "veth"]], ...]],
iov_len=32768}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) =
832
2029  close(4)                          = 0
2029  socket(AF_INET6, SOCK_DGRAM, IPPROTO_IP) = 4
2029  ioctl(4, _IOC(_IOC_NONE, 0x89, 0xf1, 0), 0x7fff4a526580) = -1
ENODEV (No such device)
2029  write(2, "add tunnel \"ip6gre0\" failed: No "..., 44) = 44
2029  close(4)                          = 0
2029  exit_group(1)                     = ?