batman_adv: batadv0: The MTU of interface macvlan2 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 1532 would solve the problem.
batman_adv: batadv0: Interface activated: macvlan2
============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
syz-executor167/5703 is trying to acquire lock:
ffff88807faf0e98 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2883 [inline]
ffff88807faf0e98 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
ffff88807faf0e98 (&dev->lock){+.+.}-{4:4}, at: netdev_sync_lower_features net/core/dev.c:11091 [inline]
ffff88807faf0e98 (&dev->lock){+.+.}-{4:4}, at: __netdev_update_features+0xd27/0x1ef0 net/core/dev.c:11261

but task is already holding lock:
ffff88807faf0e98 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2883 [inline]
ffff88807faf0e98 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
ffff88807faf0e98 (&dev->lock){+.+.}-{4:4}, at: __dev_ethtool net/ethtool/ioctl.c:3638 [inline]
ffff88807faf0e98 (&dev->lock){+.+.}-{4:4}, at: dev_ethtool+0x47e/0x29e0 net/ethtool/ioctl.c:3680
and the lock comparison function returns 0:

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&dev->lock);
  lock(&dev->lock);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

locks held by syz-executor167/5703: 2, last CPU#0:
 #0: ffffffff91276f20 (rtnl_mutex){+.+.}-{4:4}, at: __dev_ethtool net/ethtool/ioctl.c:3637 [inline]
 #0: ffffffff91276f20 (rtnl_mutex){+.+.}-{4:4}, at: dev_ethtool+0x3a0/0x29e0 net/ethtool/ioctl.c:3680
 #1: ffff88807faf0e98 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2883 [inline]
 #1: ffff88807faf0e98 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
 #1: ffff88807faf0e98 (&dev->lock){+.+.}-{4:4}, at: __dev_ethtool net/ethtool/ioctl.c:3638 [inline]
 #1: ffff88807faf0e98 (&dev->lock){+.+.}-{4:4}, at: dev_ethtool+0x47e/0x29e0 net/ethtool/ioctl.c:3680

stack backtrace:
CPU: 0 UID: 0 PID: 5703 Comm: syz-executor167 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/07/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_deadlock_bug+0x27a/0x290 kernel/locking/lockdep.c:3085
 check_deadlock kernel/locking/lockdep.c:3137 [inline]
 validate_chain kernel/locking/lockdep.c:3939 [inline]
 __lock_acquire+0x25db/0x2de0 kernel/locking/lockdep.c:5288
 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
 __mutex_lock_common kernel/locking/mutex.c:646 [inline]
 __mutex_lock+0x197/0x15a0 kernel/locking/mutex.c:821
 netdev_lock include/linux/netdevice.h:2883 [inline]
 netdev_lock_ops include/net/netdev_lock.h:42 [inline]
 netdev_sync_lower_features net/core/dev.c:11091 [inline]
 __netdev_update_features+0xd27/0x1ef0 net/core/dev.c:11261
 netdev_update_features+0x6f/0x100 net/core/dev.c:11318
 macvlan_device_event+0x62c/0x9e0 drivers/net/macvlan.c:1883
 notifier_call_chain+0x1a5/0x3d0 kernel/notifier.c:86
 call_netdevice_notifiers_extack net/core/dev.c:2351 [inline]
 call_netdevice_notifiers net/core/dev.c:2365 [inline]
 netdev_features_change+0x8d/0xd0 net/core/dev.c:1650
 dev_ethtool_locked net/ethtool/ioctl.c:3587 [inline]
 __dev_ethtool net/ethtool/ioctl.c:3645 [inline]
 dev_ethtool+0x1f21/0x29e0 net/ethtool/ioctl.c:3680
 dev_ioctl+0x392/0x1150 net/core/dev_ioctl.c:745
 sock_do_ioctl+0x23e/0x320 net/socket.c:1342
 sock_ioctl+0x57a/0x7e0 net/socket.c:1449
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f78005a0b39
Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 d8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffccd79fcd8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f78005a0b39
RDX: 00002000000005c0 RSI: 0000000000008946 RDI: 0000000000000004
RBP: 00000000000f4240 R08: 0000555570e04050 R09: 0000555570e04050
R10: 0000555570e04050 R11: 0000000000000246 R12: 00007f780060c44b
R13: 00007ffccd79fd40 R14: 0000000000000004 R15: 00007f780060c3a4
 </TASK>