syzbot

IPVS: ftp: loaded support on port[0] = 21
============================================
WARNING: possible recursive locking detected
4.19.211-syzkaller #0 Not tainted
--------------------------------------------
swapper/1/0 is trying to acquire lock:
000000005a4695cc (&port_lock_key){-.-.}, at: uart_write+0x1ce/0x6f0 drivers/tty/serial/serial_core.c:591

but task is already holding lock:
000000005a4695cc (&port_lock_key){-.-.}, at: serial8250_handle_irq.part.0+0x21/0x3d0 drivers/tty/serial/8250/8250_port.c:1876

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 swapper/1/0:
 #0: 0000000088525b6d (&(&i->lock)->rlock){-.-.}, at: spin_lock include/linux/spinlock.h:329 [inline]
 #0: 0000000088525b6d (&(&i->lock)->rlock){-.-.}, at: serial8250_interrupt+0x3a/0x240 drivers/tty/serial/8250/8250_core.c:115
 #1: 000000005a4695cc (&port_lock_key){-.-.}, at: serial8250_handle_irq.part.0+0x21/0x3d0 drivers/tty/serial/8250/8250_port.c:1876
 #2: 00000000f5223691 (&tty->ldisc_sem){++++}, at: tty_ldisc_ref+0x1d/0x80 drivers/tty/tty_ldisc.c:293

stack backtrace:
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.19.211-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1fc/0x2ef lib/dump_stack.c:118
 print_deadlock_bug kernel/locking/lockdep.c:1764 [inline]
 check_deadlock kernel/locking/lockdep.c:1808 [inline]
 validate_chain kernel/locking/lockdep.c:2404 [inline]
 __lock_acquire.cold+0x121/0x57e kernel/locking/lockdep.c:3416
 lock_acquire+0x170/0x3c0 kernel/locking/lockdep.c:3908
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0x8c/0xc0 kernel/locking/spinlock.c:152
 uart_write+0x1ce/0x6f0 drivers/tty/serial/serial_core.c:591
 n_hdlc_send_frames+0x278/0x470 drivers/tty/n_hdlc.c:403
 n_hdlc_tty_wakeup+0xa0/0xc0 drivers/tty/n_hdlc.c:479
 tty_wakeup+0xd4/0x110 drivers/tty/tty_io.c:534
 tty_port_default_wakeup+0x26/0x40 drivers/tty/tty_port.c:50
 serial8250_tx_chars+0x490/0xaf0 drivers/tty/serial/8250/8250_port.c:1813
 serial8250_handle_irq.part.0+0x31f/0x3d0 drivers/tty/serial/8250/8250_port.c:1900
 serial8250_handle_irq drivers/tty/serial/8250/8250_port.c:1873 [inline]
 serial8250_default_handle_irq+0xae/0x220 drivers/tty/serial/8250/8250_port.c:1916
 serial8250_interrupt+0x101/0x240 drivers/tty/serial/8250/8250_core.c:125
 __handle_irq_event_percpu+0x27e/0x8e0 kernel/irq/handle.c:149
 handle_irq_event_percpu kernel/irq/handle.c:189 [inline]
 handle_irq_event+0x102/0x290 kernel/irq/handle.c:206
 handle_edge_irq+0x260/0xcf0 kernel/irq/chip.c:800
 generic_handle_irq_desc include/linux/irqdesc.h:155 [inline]
 handle_irq+0x35/0x50 arch/x86/kernel/irq_64.c:87
 do_IRQ+0x93/0x1c0 arch/x86/kernel/irq.c:246
 common_interrupt+0xf/0xf arch/x86/entry/entry_64.S:670
 </IRQ>
RIP: 0010:native_safe_halt+0xe/0x10 arch/x86/include/asm/irqflags.h:61
Code: 48 89 df e8 f4 20 7f f9 e9 2e ff ff ff 48 89 df e8 e7 20 7f f9 eb 82 90 90 90 90 90 e9 07 00 00 00 0f 00 2d 14 43 4e 00 fb f4 <c3> 90 e9 07 00 00 00 0f 00 2d 04 43 4e 00 f4 c3 90 90 41 56 41 55
RSP: 0018:ffff8880b5a9fd40 EFLAGS: 00000282 ORIG_RAX: ffffffffffffffd2
RAX: 1ffffffff13e3054 RBX: dffffc0000000000 RCX: 0000000000000000
RDX: dffffc0000000000 RSI: 0000000000000001 RDI: ffff8880b5a86c44
RBP: 0000000000000001 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff89f18290
R13: 1ffff11016b53fb2 R14: 0000000000000000 R15: 0000000000000000
 arch_safe_halt arch/x86/include/asm/paravirt.h:94 [inline]
 default_idle+0x49/0x310 arch/x86/kernel/process.c:557
 cpuidle_idle_call kernel/sched/idle.c:153 [inline]
 do_idle+0x2ec/0x4b0 kernel/sched/idle.c:263
 cpu_startup_entry+0xc5/0xe0 kernel/sched/idle.c:369
 start_secondary+0x435/0x5c0 arch/x86/kernel/smpboot.c:271
 secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:243
----------------
Code disassembly (best guess):
   0:	48 89 df             	mov    %rbx,%rdi
   3:	e8 f4 20 7f f9       	callq  0xf97f20fc
   8:	e9 2e ff ff ff       	jmpq   0xffffff3b
   d:	48 89 df             	mov    %rbx,%rdi
  10:	e8 e7 20 7f f9       	callq  0xf97f20fc
  15:	eb 82                	jmp    0xffffff99
  17:	90                   	nop
  18:	90                   	nop
  19:	90                   	nop
  1a:	90                   	nop
  1b:	90                   	nop
  1c:	e9 07 00 00 00       	jmpq   0x28
  21:	0f 00 2d 14 43 4e 00 	verw   0x4e4314(%rip)        # 0x4e433c
  28:	fb                   	sti
  29:	f4                   	hlt
* 2a:	c3                   	retq <-- trapping instruction
  2b:	90                   	nop
  2c:	e9 07 00 00 00       	jmpq   0x38
  31:	0f 00 2d 04 43 4e 00 	verw   0x4e4304(%rip)        # 0x4e433c
  38:	f4                   	hlt
  39:	c3                   	retq
  3a:	90                   	nop
  3b:	90                   	nop
  3c:	41 56                	push   %r14
  3e:	41 55                	push   %r13