batman_adv: batadv0: The MTU of interface veth219 is too small (1500) to handle the transport of batman-adv packets. Packets going over this interface will be fragmented on layer2 which could impact the performance. Setting the MTU to 1560 would solve the problem.
------------[ cut here ]------------
WARNING: CPU: 0 PID: 23 at net/batman-adv/bat_iv_ogm.c:597 batadv_iv_ogm_emit net/batman-adv/bat_iv_ogm.c:597 [inline]
WARNING: CPU: 0 PID: 23 at net/batman-adv/bat_iv_ogm.c:597 batadv_iv_send_outstanding_bat_ogm_packet.cold+0x3f/0x46 net/batman-adv/bat_iv_ogm.c:1853
batman_adv: batadv0: Not using interface veth219 (retrying later): interface not active
Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 23 Comm: kworker/u4:1 Not tainted 4.19.85-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: bat_events batadv_iv_send_outstanding_bat_ogm_packet
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x197/0x210 lib/dump_stack.c:118
 panic+0x26a/0x50e kernel/panic.c:186
batman_adv: batadv0: Removing interface: veth209
 __warn.cold+0x20/0x53 kernel/panic.c:541
 report_bug+0x263/0x2b0 lib/bug.c:186
 fixup_bug arch/x86/kernel/traps.c:178 [inline]
 fixup_bug arch/x86/kernel/traps.c:173 [inline]
 do_error_trap+0x204/0x360 arch/x86/kernel/traps.c:296
 do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:316
 invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:1037
RIP: 0010:batadv_iv_ogm_emit net/batman-adv/bat_iv_ogm.c:597 [inline]
RIP: 0010:batadv_iv_send_outstanding_bat_ogm_packet.cold+0x3f/0x46 net/batman-adv/bat_iv_ogm.c:1853
Code: a4 ff ff e8 43 15 97 fa 48 c7 c7 40 64 fb 87 e8 db 79 81 fa e9 7d a4 ff ff e8 2d 15 97 fa 48 c7 c7 00 61 fb 87 e8 c5 79 81 fa <0f> 0b e9 65 a4 ff ff e8 15 15 97 fa 48 c7 c7 00 61 fb 87 e8 ad 79
RSP: 0018:ffff8880aa39fcc8 EFLAGS: 00010282
RAX: 0000000000000024 RBX: ffff8880a41d3488 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff815595d6 RDI: ffffed1015473f8b
RBP: ffff8880aa39fd30 R08: 0000000000000024 R09: ffffed1015d05079
R10: ffffed1015d05078 R11: ffff8880ae8283c7 R12: ffff88809a3dd280
R13: ffff88809f965200 R14: ffff8880a41d3440 R15: ffff88809a3dd280
 process_one_work+0x989/0x1750 kernel/workqueue.c:2153
 worker_thread+0x98/0xe40 kernel/workqueue.c:2296
 kthread+0x354/0x420 kernel/kthread.c:246
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415
Kernel Offset: disabled
Rebooting in 86400 seconds..