batman_adv: batadv0: Interface activated: batadv_slave_1 IPv6: ADDRCONF(NETDEV_CHANGE): batadv_slave_1: link becomes ready IPv6: ADDRCONF(NETDEV_CHANGE): veth1_to_batadv: link becomes ready ============================================ WARNING: possible recursive locking detected 4.14.172-syzkaller #0 Not tainted -------------------------------------------- swapper/0/0 is trying to acquire lock: (&port_lock_key){-.-.}, at: [] uart_write+0x109/0x4e0 drivers/tty/serial/serial_core.c:604 but task is already holding lock: (&port_lock_key){-.-.}, at: [] serial8250_handle_irq.part.0+0x20/0x240 drivers/tty/serial/8250/8250_port.c:1872 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/0/0: #0: (&(&i->lock)->rlock){-.-.}, at: [] spin_lock include/linux/spinlock.h:317 [inline] #0: (&(&i->lock)->rlock){-.-.}, at: [] serial8250_interrupt+0x2b/0x1a0 drivers/tty/serial/8250/8250_core.c:119 #1: (&port_lock_key){-.-.}, at: [] serial8250_handle_irq.part.0+0x20/0x240 drivers/tty/serial/8250/8250_port.c:1872 #2: (&tty->ldisc_sem){++++}, at: [] tty_ldisc_ref+0x1b/0x80 drivers/tty/tty_ldisc.c:305 stack backtrace: CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.14.172-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:17 [inline] dump_stack+0x13e/0x194 lib/dump_stack.c:58 print_deadlock_bug kernel/locking/lockdep.c:1796 [inline] check_deadlock kernel/locking/lockdep.c:1843 [inline] validate_chain kernel/locking/lockdep.c:2444 [inline] __lock_acquire.cold+0x2bf/0x8dc kernel/locking/lockdep.c:3487 lock_acquire+0x170/0x3f0 kernel/locking/lockdep.c:3994 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline] _raw_spin_lock_irqsave+0x8c/0xbf kernel/locking/spinlock.c:160 uart_write+0x109/0x4e0 drivers/tty/serial/serial_core.c:604 n_hdlc_send_frames+0x23c/0x3f0 drivers/tty/n_hdlc.c:404 n_hdlc_tty_wakeup+0x95/0xb0 drivers/tty/n_hdlc.c:480 tty_wakeup+0xc3/0xf0 drivers/tty/tty_io.c:533 tty_port_default_wakeup+0x26/0x40 drivers/tty/tty_port.c:49 serial8250_tx_chars+0x400/0x9e0 drivers/tty/serial/8250/8250_port.c:1810 serial8250_handle_irq.part.0+0x1f8/0x240 drivers/tty/serial/8250/8250_port.c:1883 serial8250_handle_irq drivers/tty/serial/8250/8250_port.c:1869 [inline] serial8250_default_handle_irq+0x96/0x110 drivers/tty/serial/8250/8250_port.c:1899 serial8250_interrupt+0xe4/0x1a0 drivers/tty/serial/8250/8250_core.c:129 __handle_irq_event_percpu+0x125/0x7e0 kernel/irq/handle.c:147 handle_irq_event_percpu+0x66/0x120 kernel/irq/handle.c:187 handle_irq_event+0xa2/0x12d kernel/irq/handle.c:204 handle_edge_irq+0x215/0x810 kernel/irq/chip.c:770 generic_handle_irq_desc include/linux/irqdesc.h:159 [inline] handle_irq+0x35/0x50 arch/x86/kernel/irq_64.c:87 do_IRQ+0x93/0x1d0 arch/x86/kernel/irq.c:230 common_interrupt+0x8f/0x8f arch/x86/entry/entry_64.S:576 RIP: 0010:native_safe_halt+0xe/0x10 arch/x86/include/asm/irqflags.h:61 RSP: 0018:ffffffff87c07e78 EFLAGS: 00000282 ORIG_RAX: ffffffffffffffc8 RAX: 1ffffffff0fa2ce4 RBX: dffffc0000000000 RCX: 0000000000000000 RDX: dffffc0000000000 RSI: 0000000000000001 RDI: ffffffff87c76abc RBP: ffffffff87d16710 R08: 1ffffffff1124101 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: fffffbfff0f8ec48 R13: ffffffff87c76240 R14: 0000000000000000 R15: 0000000000000000 arch_safe_halt arch/x86/include/asm/paravirt.h:94 [inline] default_idle+0x47/0x370 arch/x86/kernel/process.c:566 cpuidle_idle_call kernel/sched/idle.c:156 [inline] do_idle+0x250/0x3c0 kernel/sched/idle.c:246 cpu_startup_entry+0x14/0x20 kernel/sched/idle.c:351 start_kernel+0x659/0x676 init/main.c:708 secondary_startup_64+0xa5/0xb0 arch/x86/kernel/head_64.S:240