batman_adv: batadv0: The MTU of interface batadv_slave_1 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.
batman_adv: batadv0: Not using interface batadv_slave_1 (retrying later): interface not active
device hsr_slave_0 entered promiscuous mode
device hsr_slave_1 entered promiscuous mode
============================================
WARNING: possible recursive locking detected
5.11.0-rc5-next-20210127-syzkaller #0 Not tainted
--------------------------------------------
syz-executor.0/8437 is trying to acquire lock:
ffff88801b1aa5e8 (&rdev->wiphy.mtx){+.+.}-{3:3}, at: wiphy_lock include/net/cfg80211.h:5267 [inline]
ffff88801b1aa5e8 (&rdev->wiphy.mtx){+.+.}-{3:3}, at: cfg80211_netdev_notifier_call+0x615/0x1180 net/wireless/core.c:1393

but task is already holding lock:
ffff88801b1aa5e8 (&rdev->wiphy.mtx){+.+.}-{3:3}, at: wiphy_lock include/net/cfg80211.h:5267 [inline]
ffff88801b1aa5e8 (&rdev->wiphy.mtx){+.+.}-{3:3}, at: virt_wifi_newlink+0x4cb/0x940 drivers/net/wireless/virt_wifi.c:540

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

       CPU0
       ----
  lock(&rdev->wiphy.mtx);
  lock(&rdev->wiphy.mtx);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by syz-executor.0/8437:
 #0: ffffffff8cc71b08 (rtnl_mutex){+.+.}-{3:3}, at: rtnl_lock net/core/rtnetlink.c:72 [inline]
 #0: ffffffff8cc71b08 (rtnl_mutex){+.+.}-{3:3}, at: rtnetlink_rcv_msg+0x3f9/0xad0 net/core/rtnetlink.c:5550
 #1: ffff88801b1aa5e8 (&rdev->wiphy.mtx){+.+.}-{3:3}, at: wiphy_lock include/net/cfg80211.h:5267 [inline]
 #1: ffff88801b1aa5e8 (&rdev->wiphy.mtx){+.+.}-{3:3}, at: virt_wifi_newlink+0x4cb/0x940 drivers/net/wireless/virt_wifi.c:540

stack backtrace:
CPU: 0 PID: 8437 Comm: syz-executor.0 Not tainted 5.11.0-rc5-next-20210127-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x107/0x163 lib/dump_stack.c:120
 print_deadlock_bug kernel/locking/lockdep.c:2829 [inline]
 check_deadlock kernel/locking/lockdep.c:2872 [inline]
 validate_chain kernel/locking/lockdep.c:3661 [inline]
 __lock_acquire.cold+0x14c/0x3b4 kernel/locking/lockdep.c:4899
 lock_acquire kernel/locking/lockdep.c:5509 [inline]
 lock_acquire+0x1a8/0x720 kernel/locking/lockdep.c:5474
 __mutex_lock_common kernel/locking/mutex.c:956 [inline]
 __mutex_lock+0x134/0x1110 kernel/locking/mutex.c:1103
 wiphy_lock include/net/cfg80211.h:5267 [inline]
 cfg80211_netdev_notifier_call+0x615/0x1180 net/wireless/core.c:1393
 notifier_call_chain+0xb5/0x200 kernel/notifier.c:83
 call_netdevice_notifiers_info+0xb5/0x130 net/core/dev.c:2040
 call_netdevice_notifiers_extack net/core/dev.c:2052 [inline]
 call_netdevice_notifiers net/core/dev.c:2066 [inline]
 register_netdevice+0x1034/0x14a0 net/core/dev.c:10008
 virt_wifi_newlink+0x4d3/0x940 drivers/net/wireless/virt_wifi.c:541
 __rtnl_newlink+0x108b/0x16e0 net/core/rtnetlink.c:3443
 rtnl_newlink+0x64/0xa0 net/core/rtnetlink.c:3491
 rtnetlink_rcv_msg+0x44e/0xad0 net/core/rtnetlink.c:5553
 netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2494
 netlink_unicast_kernel net/netlink/af_netlink.c:1304 [inline]
 netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1330
 netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1919
 sock_sendmsg_nosec net/socket.c:654 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:674
 __sys_sendto+0x21c/0x320 net/socket.c:1977
 __do_sys_sendto net/socket.c:1989 [inline]
 __se_sys_sendto net/socket.c:1985 [inline]
 __x64_sys_sendto+0xdd/0x1b0 net/socket.c:1985
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x417c97
Code: 2c 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 81 19 00 00 c3 48 83 ec 08 e8 e7 fa ff ff 48 89 04 24 49 89 ca b8 2c 00 00 00 0f 05 <48> 8b 3c 24 48 89 c2 e8 2d fb ff ff 48 89 d0 48 83 c4 08 48 3d 01
RSP: 002b:00007fff10930a60 EFLAGS: 00000293 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00000000016b4300 RCX: 0000000000417c97
RDX: 000000000000004c RSI: 00000000016b4350 RDI: 0000000000000003
RBP: 0000000000000000 R08: 00007fff10930a70 R09: 000000000000000c
R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000000
R13: 0000000000000000 R14: 00000000016b4350 R15: 0000000000000003