RDX: 0000000000000000 RSI: 0000000020000180 RDI: 0000000000000004
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f199f0736d4
R13: 00000000004ca9ed R14: 00000000004e3e60 R15: 0000000000000009
============================================
WARNING: possible recursive locking detected
4.19.94-syzkaller #0 Not tainted
--------------------------------------------
syz-executor.0/11876 is trying to acquire lock:
00000000b230beda (rtnl_mutex){+.+.}, at: rtnl_lock+0x17/0x20 net/core/rtnetlink.c:77

but task is already holding lock:
00000000b230beda (rtnl_mutex){+.+.}, at: rtnl_lock net/core/rtnetlink.c:77 [inline]
00000000b230beda (rtnl_mutex){+.+.}, at: rtnetlink_rcv_msg+0x40a/0xb00 net/core/rtnetlink.c:4765

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

       CPU0
       ----
  lock(rtnl_mutex);
  lock(rtnl_mutex);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

1 lock held by syz-executor.0/11876:
 #0: 00000000b230beda (rtnl_mutex){+.+.}, at: rtnl_lock net/core/rtnetlink.c:77 [inline]
 #0: 00000000b230beda (rtnl_mutex){+.+.}, at: rtnetlink_rcv_msg+0x40a/0xb00 net/core/rtnetlink.c:4765

stack backtrace:
CPU: 1 PID: 11876 Comm: syz-executor.0 Not tainted 4.19.94-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x197/0x210 lib/dump_stack.c:118
 print_deadlock_bug kernel/locking/lockdep.c:1759 [inline]
 check_deadlock kernel/locking/lockdep.c:1803 [inline]
 validate_chain kernel/locking/lockdep.c:2399 [inline]
 __lock_acquire.cold+0x20f/0x4a7 kernel/locking/lockdep.c:3411
 lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:3903
 __mutex_lock_common kernel/locking/mutex.c:925 [inline]
 __mutex_lock+0xf7/0x1300 kernel/locking/mutex.c:1072
 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1087
 rtnl_lock+0x17/0x20 net/core/rtnetlink.c:77
 hsr_dev_destroy+0x1f/0xc0 net/hsr/hsr_device.c:371
 register_netdevice+0xc3c/0xff0 net/core/dev.c:8779
 hsr_dev_finalize+0x4fc/0x780 net/hsr/hsr_device.c:489
 hsr_newlink+0x26b/0x380 net/hsr/hsr_netlink.c:72
 rtnl_newlink+0x1042/0x1600 net/core/rtnetlink.c:3132
 rtnetlink_rcv_msg+0x463/0xb00 net/core/rtnetlink.c:4768
 netlink_rcv_skb+0x17d/0x460 net/netlink/af_netlink.c:2454
 rtnetlink_rcv+0x1d/0x30 net/core/rtnetlink.c:4786
 netlink_unicast_kernel net/netlink/af_netlink.c:1317 [inline]
 netlink_unicast+0x53a/0x730 net/netlink/af_netlink.c:1343
 netlink_sendmsg+0x8ae/0xd70 net/netlink/af_netlink.c:1908
 sock_sendmsg_nosec net/socket.c:622 [inline]
 sock_sendmsg+0xd7/0x130 net/socket.c:632
 ___sys_sendmsg+0x803/0x920 net/socket.c:2115
 __sys_sendmsg+0x105/0x1d0 net/socket.c:2153
 __do_sys_sendmsg net/socket.c:2162 [inline]
 __se_sys_sendmsg net/socket.c:2160 [inline]
 __x64_sys_sendmsg+0x78/0xb0 net/socket.c:2160
 do_syscall_64+0xfd/0x620 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45af49
Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f199f072c78 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f199f072c90 RCX: 000000000045af49
RDX: 0000000000000000 RSI: 0000000020000180 RDI: 0000000000000004
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f199f0736d4
R13: 00000000004ca9ed R14: 00000000004e3e60 R15: 0000000000000009