============================================
WARNING: possible recursive locking detected
5.6.0-rc3-next-20200228-syzkaller #0 Not tainted
--------------------------------------------
init/1 is trying to acquire lock:
ffffffff8d0cd6b0 (&port_lock_key){-.-.}, at: uart_write+0x1c7/0x660 drivers/tty/serial/serial_core.c:592

but task is already holding lock:
ffffffff8d0cd6b0 (&port_lock_key){-.-.}, at: serial8250_handle_irq.part.0+0x21/0x290 drivers/tty/serial/8250/8250_port.c:1822

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

4 locks held by init/1:
 #0: ffffffff89a64088 (remove_cache_srcu){....}, at: quarantine_reduce+0x60/0x190 mm/kasan/quarantine.c:262
 #1: ffff8880a753aeb0 (&(&i->lock)->rlock){-.-.}, at: spin_lock include/linux/spinlock.h:338 [inline]
 #1: ffff8880a753aeb0 (&(&i->lock)->rlock){-.-.}, at: serial8250_interrupt+0x27/0x190 drivers/tty/serial/8250/8250_core.c:116
 #2: ffffffff8d0cd6b0 (&port_lock_key){-.-.}, at: serial8250_handle_irq.part.0+0x21/0x290 drivers/tty/serial/8250/8250_port.c:1822
 #3: ffff888094540090 (&tty->ldisc_sem){++++}, at: tty_ldisc_ref+0x1d/0x80 drivers/tty/tty_ldisc.c:288

stack backtrace:
CPU: 1 PID: 1 Comm: init Not tainted 5.6.0-rc3-next-20200228-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x188/0x20d lib/dump_stack.c:118
 print_deadlock_bug kernel/locking/lockdep.c:2376 [inline]
 check_deadlock kernel/locking/lockdep.c:2417 [inline]
 validate_chain kernel/locking/lockdep.c:3187 [inline]
 __lock_acquire.cold+0x172/0x2c1 kernel/locking/lockdep.c:4190
 lock_acquire+0x197/0x420 kernel/locking/lockdep.c:4720
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0x8c/0xbf kernel/locking/spinlock.c:159
 uart_write+0x1c7/0x660 drivers/tty/serial/serial_core.c:592
 n_hdlc_send_frames+0x22d/0x3d0 drivers/tty/n_hdlc.c:291
 tty_wakeup+0xe1/0x120 drivers/tty/tty_io.c:536
 tty_port_default_wakeup+0x26/0x40 drivers/tty/tty_port.c:50
 serial8250_tx_chars+0x48f/0xae0 drivers/tty/serial/8250/8250_port.c:1760
 serial8250_handle_irq.part.0+0x24b/0x290 drivers/tty/serial/8250/8250_port.c:1833
 serial8250_handle_irq drivers/tty/serial/8250/8250_port.c:1819 [inline]
 serial8250_default_handle_irq+0xb5/0x140 drivers/tty/serial/8250/8250_port.c:1849
 serial8250_interrupt+0xe6/0x190 drivers/tty/serial/8250/8250_core.c:126
 __handle_irq_event_percpu+0x15d/0x950 kernel/irq/handle.c:149
 handle_irq_event_percpu+0x76/0x160 kernel/irq/handle.c:189
 handle_irq_event+0xa2/0x12d kernel/irq/handle.c:206
 handle_edge_irq+0x24b/0x8c0 kernel/irq/chip.c:830
 generic_handle_irq_desc include/linux/irqdesc.h:156 [inline]
 do_IRQ+0xd9/0x280 arch/x86/kernel/irq.c:250
 common_interrupt+0xf/0xf arch/x86/entry/entry_64.S:607
 </IRQ>
RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:752 [inline]
RIP: 0010:qlink_free mm/kasan/quarantine.c:151 [inline]
RIP: 0010:qlist_free_all+0xfc/0x140 mm/kasan/quarantine.c:167
Code: 50 08 48 8d 4a ff 83 e2 01 48 0f 45 c1 4c 8b 70 18 e9 40 ff ff ff e8 a3 4d c8 ff 48 83 3d e3 0d e4 07 00 74 36 4c 89 ff 57 9d <0f> 1f 44 00 00 4d 85 e4 75 9e 49 c7 45 08 00 00 00 00 49 c7 45 00
RSP: 0018:ffffc90000c7fb98 EFLAGS: 00000286 ORIG_RAX: ffffffffffffffda
RAX: 0000000000000007 RBX: ffff8880948545c0 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffff8880a958c8e0 RDI: 0000000000000286
RBP: 0000000000000000 R08: ffff8880a958c040 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8880970c1800
R13: ffffc90000c7fbd0 R14: ffff8880aa0001c0 R15: 0000000000000286
 quarantine_reduce+0x159/0x190 mm/kasan/quarantine.c:260
 __kasan_kmalloc.constprop.0+0x97/0xd0 mm/kasan/common.c:473
 slab_post_alloc_hook mm/slab.h:586 [inline]
 slab_alloc mm/slab.c:3320 [inline]
 kmem_cache_alloc+0x11b/0x730 mm/slab.c:3484
 getname_flags fs/namei.c:138 [inline]
 getname_flags+0xd2/0x5b0 fs/namei.c:128
 user_path_at_empty+0x2a/0x50 fs/namei.c:2746
 user_path_at include/linux/namei.h:58 [inline]
 vfs_statx+0x119/0x1e0 fs/stat.c:197
 vfs_stat include/linux/fs.h:3273 [inline]
 __do_sys_newstat+0x96/0x120 fs/stat.c:351
 do_syscall_64+0xf6/0x790 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x7ff41139dc65
Code: 00 00 00 e8 5d 01 00 00 48 83 c4 18 c3 90 90 90 90 90 90 90 90 83 ff 01 48 89 f0 77 18 48 89 c7 48 89 d6 b8 04 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 17 f3 c3 90 48 8b 05 a1 51 2b 00 64 c7 00 16
RSP: 002b:00007ffcbd5dcc88 EFLAGS: 00000246 ORIG_RAX: 0000000000000004
RAX: ffffffffffffffda RBX: 00007ffcbd5dcec0 RCX: 00007ff41139dc65
RDX: 00007ffcbd5dcec0 RSI: 00007ffcbd5dcec0 RDI: 0000000000407545
RBP: 0000000000000000 R08: 0000000000e53240 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00007ffcbd5dd3c0 R14: 0000000000000000 R15: 0000000000000000