WARNING: suspicious RCU usage in vxlan

Kernel	Title	Rank 🛈	Repro	Cause bisect	Fix bisect	Count	Last	Reported	Patched	Status
upstream	WARNING: suspicious RCU usage in vxlan_xmit net	4	C	error		1	1859d	1859d	20/29	fixed on 2021/11/10 00:50

netlink: 12 bytes leftover after parsing attributes in process `syz-executor764'.
netlink: 'syz-executor764': attribute type 11 has an invalid length.
netlink: 16 bytes leftover after parsing attributes in process `syz-executor764'.
=============================
WARNING: suspicious RCU usage
4.19.196-syzkaller #0 Not tainted
-----------------------------
include/net/addrconf.h:340 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
3 locks held by kworker/0:1/14:
 #0: 0000000096600449 ((wq_completion)"events"){+.+.}, at: process_one_work+0x767/0x1570 kernel/workqueue.c:2124
 #1: 00000000e4b4d003 ((work_completion)(&port->wq)){+.+.}, at: process_one_work+0x79c/0x1570 kernel/workqueue.c:2128
 #2: 00000000b451db01 (rcu_read_lock_bh){....}, at: __dev_queue_xmit+0x1e2/0x2e00 net/core/dev.c:3773

stack backtrace:
CPU: 0 PID: 14 Comm: kworker/0:1 Not tainted 4.19.196-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events ipvlan_process_multicast
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1fc/0x2ef lib/dump_stack.c:118
 __in6_dev_get include/net/addrconf.h:340 [inline]
 neigh_reduce drivers/net/vxlan.c:1685 [inline]
 vxlan_xmit+0x2b3b/0x4250 drivers/net/vxlan.c:2343
 __netdev_start_xmit include/linux/netdevice.h:4345 [inline]
 netdev_start_xmit include/linux/netdevice.h:4359 [inline]
 xmit_one net/core/dev.c:3256 [inline]
 dev_hard_start_xmit+0x1a8/0x920 net/core/dev.c:3272
 __dev_queue_xmit+0x269d/0x2e00 net/core/dev.c:3838
 ipvlan_process_multicast+0xa19/0xcb0 drivers/net/ipvlan/ipvlan_core.c:292
 process_one_work+0x864/0x1570 kernel/workqueue.c:2153
 worker_thread+0x64c/0x1130 kernel/workqueue.c:2296