============================================
WARNING: possible recursive locking detected
5.16.0-rc2-next-20211125-syzkaller #0 Not tainted
--------------------------------------------
systemd-udevd/2969 is trying to acquire lock:
ffffffff9079b770 (&port_lock_key){-.-.}-{2:2}, at: uart_write+0x12c/0x570 drivers/tty/serial/serial_core.c:577

but task is already holding lock:
ffffffff9079b770 (&port_lock_key){-.-.}-{2:2}, at: serial8250_handle_irq.part.0+0x21/0x3d0 drivers/tty/serial/8250/8250_port.c:1908

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

       CPU0
       ----
  lock(&port_lock_key);
  lock(&port_lock_key);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

3 locks held by systemd-udevd/2969:
 #0: ffff8880742a04b0 (&i->lock){-.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:354 [inline]
 #0: ffff8880742a04b0 (&i->lock){-.-.}-{2:2}, at: serial8250_interrupt+0x3a/0x200 drivers/tty/serial/8250/8250_core.c:116
 #1: ffffffff9079b770 (&port_lock_key){-.-.}-{2:2}, at: serial8250_handle_irq.part.0+0x21/0x3d0 drivers/tty/serial/8250/8250_port.c:1908
 #2: ffff8880196bb098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref+0x1d/0x80 drivers/tty/tty_ldisc.c:273

stack backtrace:
CPU: 1 PID: 2969 Comm: systemd-udevd Not tainted 5.16.0-rc2-next-20211125-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
 print_deadlock_bug kernel/locking/lockdep.c:2956 [inline]
 check_deadlock kernel/locking/lockdep.c:2999 [inline]
 validate_chain kernel/locking/lockdep.c:3788 [inline]
 __lock_acquire.cold+0x149/0x3ab kernel/locking/lockdep.c:5027
 lock_acquire kernel/locking/lockdep.c:5637 [inline]
 lock_acquire+0x1ab/0x510 kernel/locking/lockdep.c:5602
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0x39/0x50 kernel/locking/spinlock.c:162
 uart_write+0x12c/0x570 drivers/tty/serial/serial_core.c:577
 n_hdlc_send_frames+0x24b/0x490 drivers/tty/n_hdlc.c:290
 tty_wakeup+0xe1/0x120 drivers/tty/tty_io.c:534
 tty_port_default_wakeup+0x26/0x40 drivers/tty/tty_port.c:51
 serial8250_tx_chars+0x4f3/0xad0 drivers/tty/serial/8250/8250_port.c:1845
 serial8250_handle_irq.part.0+0x328/0x3d0 drivers/tty/serial/8250/8250_port.c:1932
 serial8250_handle_irq drivers/tty/serial/8250/8250_port.c:1905 [inline]
 serial8250_default_handle_irq+0xb2/0x220 drivers/tty/serial/8250/8250_port.c:1949
 serial8250_interrupt+0xfd/0x200 drivers/tty/serial/8250/8250_core.c:126
 __handle_irq_event_percpu+0x303/0x8f0 kernel/irq/handle.c:158
 handle_irq_event_percpu kernel/irq/handle.c:198 [inline]
 handle_irq_event+0x102/0x280 kernel/irq/handle.c:215
 handle_edge_irq+0x25f/0xd00 kernel/irq/chip.c:822
 generic_handle_irq_desc include/linux/irqdesc.h:158 [inline]
 handle_irq arch/x86/kernel/irq.c:231 [inline]
 __common_interrupt+0x9d/0x210 arch/x86/kernel/irq.c:250
 common_interrupt+0x4d/0xc0 arch/x86/kernel/irq.c:240
 asm_common_interrupt+0x1e/0x40 arch/x86/include/asm/idtentry.h:629
RIP: 0033:0x7f965506e4b0
Code: 86 fa ff ff 66 0f 1f 44 00 00 48 8d 3d 8a 27 12 00 48 83 ec 08 e8 70 fa ff ff 85 c0 0f 94 c0 48 83 c4 08 0f b6 c0 c3 0f 1f 00 <55> 48 89 e5 41 57 41 56 41 55 41 54 53 48 81 ec c8 00 00 00 48 85
RSP: 002b:00007ffcc59a4ee8 EFLAGS: 00000246
RAX: 0000000000000000 RBX: 00007ffcc59a4f65 RCX: 0000000000000000
RDX: 00000000ffffffff RSI: 0000000000000000 RDI: 000055b8837d09e0
RBP: 00007ffcc59a4f20 R08: 000055b8837e47b0 R09: 0000000000000000
R10: 0000000000000063 R11: 0000000000000202 R12: 00007ffcc59a4f60
R13: 000055b8837e4610 R14: 000055b8837d09e0 R15: 00007ffcc59a60f0
 </TASK>