syzbot

netdevsim netdevsim8 eth1: unset [0, 0] type 1 family 0 port 8472 - 0
netdevsim netdevsim8 eth2: unset [0, 0] type 1 family 0 port 8472 - 0
netdevsim netdevsim8 eth3: unset [0, 0] type 1 family 0 port 8472 - 0
============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
syz.8.1993/12388 is trying to acquire lock:
ffffffff8d43c848 (rtnl_mutex){+.+.}-{3:3}, at: ip_mc_drop_socket+0x7b/0x270 net/ipv4/igmp.c:2702

but task is already holding lock:
ffffffff8d43c848 (rtnl_mutex){+.+.}-{3:3}, at: rtnl_lock net/core/rtnetlink.c:72 [inline]
ffffffff8d43c848 (rtnl_mutex){+.+.}-{3:3}, at: rtnetlink_rcv_msg+0x7ee/0xf30 net/core/rtnetlink.c:5681

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.8.1993/12388:
 #0: ffffffff8d43c848 (rtnl_mutex){+.+.}-{3:3}, at: rtnl_lock net/core/rtnetlink.c:72 [inline]
 #0: ffffffff8d43c848 (rtnl_mutex){+.+.}-{3:3}, at: rtnetlink_rcv_msg+0x7ee/0xf30 net/core/rtnetlink.c:5681

stack backtrace:
CPU: 0 PID: 12388 Comm: syz.8.1993 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 __lock_acquire+0x1236/0x7d10 kernel/locking/lockdep.c:-1
 lock_acquire+0x19e/0x400 kernel/locking/lockdep.c:5623
 __mutex_lock_common+0x1e3/0x2400 kernel/locking/mutex.c:596
 __mutex_lock kernel/locking/mutex.c:729 [inline]
 mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
 ip_mc_drop_socket+0x7b/0x270 net/ipv4/igmp.c:2702
 inet_release+0x47/0x180 net/ipv4/af_inet.c:419
 __sock_release net/socket.c:651 [inline]
 sock_release+0x7b/0x140 net/socket.c:679
 vxlan_sock_release+0x385/0x400 drivers/net/vxlan/vxlan_core.c:1637
 vxlan_stop+0xf62/0x1090 drivers/net/vxlan/vxlan_core.c:3149
 __dev_close_many+0x1d3/0x2b0 net/core/dev.c:1634
 __dev_close net/core/dev.c:1646 [inline]
 __dev_change_flags+0x2d8/0x6a0 net/core/dev.c:8864
 dev_change_flags+0x82/0x1a0 net/core/dev.c:8937
 do_setlink+0xcdb/0x3d60 net/core/rtnetlink.c:2781
 rtnl_group_changelink net/core/rtnetlink.c:3298 [inline]
 __rtnl_newlink net/core/rtnetlink.c:3462 [inline]
 rtnl_newlink+0xf8d/0x1a50 net/core/rtnetlink.c:3574
 rtnetlink_rcv_msg+0x844/0xf30 net/core/rtnetlink.c:5684
 netlink_rcv_skb+0x1f5/0x440 net/netlink/af_netlink.c:2507
 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
 netlink_unicast+0x774/0x920 net/netlink/af_netlink.c:1344
 netlink_sendmsg+0x8ba/0xbe0 net/netlink/af_netlink.c:1918
 sock_sendmsg_nosec net/socket.c:706 [inline]
 __sock_sendmsg net/socket.c:718 [inline]
 ____sys_sendmsg+0x5b7/0x8f0 net/socket.c:2445
 ___sys_sendmsg+0x236/0x2e0 net/socket.c:2499
 __sys_sendmsg net/socket.c:2528 [inline]
 __do_sys_sendmsg net/socket.c:2537 [inline]
 __se_sys_sendmsg+0x1af/0x290 net/socket.c:2535
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f8f75160629
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f8f733ba028 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f8f753d9fa0 RCX: 00007f8f75160629
RDX: 0000000004000000 RSI: 0000200000000240 RDI: 0000000000000005
RBP: 00007f8f751f6b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f8f753da038 R14: 00007f8f753d9fa0 R15: 00007ffff65a33f8
 </TASK>