On 26/1/6 8:22, Jakub Kicinski wrote:
On Wed, 31 Dec 2025 11:54:19 +0800 Chen Zhen wrote:
quoted
skbuff: skb_under_panic: text:ffffffff95b33e66 len:90 put:14 head:ffff915ac1967440 data:ffff915ac196743e tail:0x58 end:0x180 dev:br0.10
------------[ cut here ]------------
kernel BUG at net/core/skbuff.c:197!
Call Trace:
<TASK>
skb_push+0x39/0x40
eth_header+0x26/0xb0
vlan_dev_hard_header+0x58/0x130 [8021q]
neigh_connected_output+0xae/0x100
ip6_finish_output2+0x2cc/0x650
? nf_hook_slow+0x41/0xc0
ip6_finish_output+0x27/0xd0
ndisc_send_skb+0x1d0/0x370
? __pfx_dst_output+0x10/0x10
ndisc_send_ns+0x5a/0xb0
addrconf_dad_work+0x2b5/0x380
process_one_work+0x17f/0x320
Please run this stack trace thru script/decode_stacktrace
and you can cut off here, no need to include functions
below process_one_work, they are irrelevant.
quoted
worker_thread+0x26d/0x2f0
? __pfx_worker_thread+0x10/0x10
kthread+0xcc/0x100
? __pfx_kthread+0x10/0x10
ret_from_fork+0x30/0x50
? __pfx_kthread+0x10/0x10
ret_from_fork_asm+0x1b/0x30
</TASK>
This bug can be easily reproduced by these steps:
ip link add veth0 type veth peer name veth1
ip link set veth0 up
ip link set veth1 up
ethtool -K veth0 tx-vlan-hw-insert off
# vlandev.header_ops = vlan_header_ops, hard_header_len = 18(hard_header_len + VLAN_HLEN)
ip link add link veth0 name veth0.10 type vlan id 10 reorder_hdr off
ip addr add 192.168.10.1/24 dev veth0.10
ip link set veth0.10 up
# vlandev.hard_header_len = 14(hard_header_len)
ethtool -K veth0 tx-vlan-hw-insert on
# Panic!
Instead of putting this in the commit message please add a selftest
which will automatically catch re-occurrence of the issue.
quoted
The reason is that when NETIF_F_HW_VLAN_CTAG_TX is off, vlandev.hard_header_len will be set to
dev->hard_header_len since commit 029f5fc31cdb ("8021q: set hard_header_len when VLAN offload features
are toggled"), but the header_ops remains unchanged. Then neigh_connected_output() will call
vlan_dev_hard_header() and panic in skb_push() because reorder_hdr is off.
Please wrap commit messages at 70 columns.
Thanks for your patient review and I will send patch v2 soon.
Best regards,
Chen Zhen