============================================ WARNING: possible recursive locking detected 4.14.288-syzkaller #0 Not tainted -------------------------------------------- syz-fuzzer/7995 is trying to acquire lock: (&port_lock_key){-.-.}, at: [] uart_write+0x109/0x560 drivers/tty/serial/serial_core.c:611 but task is already holding lock: (&port_lock_key){-.-.}, at: [] serial8250_handle_irq.part.0+0x20/0x330 drivers/tty/serial/8250/8250_port.c:1891 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 syz-fuzzer/7995: #0: (&(&i->lock)->rlock){-.-.}, at: [] spin_lock include/linux/spinlock.h:317 [inline] #0: (&(&i->lock)->rlock){-.-.}, at: [] serial8250_interrupt+0x3a/0x210 drivers/tty/serial/8250/8250_core.c:119 #1: (&port_lock_key){-.-.}, at: [] serial8250_handle_irq.part.0+0x20/0x330 drivers/tty/serial/8250/8250_port.c:1891 #2: (&tty->ldisc_sem){++++}, at: [] tty_ldisc_ref+0x1b/0x80 drivers/tty/tty_ldisc.c:305 stack backtrace: CPU: 1 PID: 7995 Comm: syz-fuzzer Not tainted 4.14.288-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/29/2022 Call Trace: __dump_stack lib/dump_stack.c:17 [inline] dump_stack+0x1b2/0x281 lib/dump_stack.c:58 print_deadlock_bug kernel/locking/lockdep.c:1800 [inline] check_deadlock kernel/locking/lockdep.c:1847 [inline] validate_chain kernel/locking/lockdep.c:2448 [inline] __lock_acquire.cold+0x180/0x97c kernel/locking/lockdep.c:3491 lock_acquire+0x170/0x3f0 kernel/locking/lockdep.c:3998 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline] _raw_spin_lock_irqsave+0x8c/0xc0 kernel/locking/spinlock.c:160 uart_write+0x109/0x560 drivers/tty/serial/serial_core.c:611 n_hdlc_send_frames+0x241/0x410 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+0x3fe/0xc70 drivers/tty/serial/8250/8250_port.c:1828 serial8250_handle_irq.part.0+0x28d/0x330 drivers/tty/serial/8250/8250_port.c:1915 serial8250_handle_irq drivers/tty/serial/8250/8250_port.c:1888 [inline] serial8250_default_handle_irq+0x8a/0x1f0 drivers/tty/serial/8250/8250_port.c:1931 serial8250_interrupt+0xf3/0x210 drivers/tty/serial/8250/8250_core.c:129 __handle_irq_event_percpu+0xee/0x7f0 kernel/irq/handle.c:147 handle_irq_event_percpu kernel/irq/handle.c:187 [inline] handle_irq_event+0xed/0x240 kernel/irq/handle.c:204 handle_edge_irq+0x224/0xc40 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+0x93/0x93 arch/x86/entry/entry_64.S:576 RIP: 0010:__raw_spin_unlock_irq include/linux/spinlock_api_smp.h:169 [inline] RIP: 0010:_raw_spin_unlock_irq+0x50/0x80 kernel/locking/spinlock.c:200 RSP: 0018:ffff8880936ff8e0 EFLAGS: 00000282 ORIG_RAX: ffffffffffffffc8 RAX: 1ffffffff11e1343 RBX: ffff8880929c8040 RCX: 0000000000000000 RDX: dffffc0000000000 RSI: 0000000000000001 RDI: ffff8880929c88c4 RBP: ffff8880ba534400 R08: ffffffff8b9a1e98 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: ffff8880ba534400 R13: ffff88809bd20580 R14: 0000000000000000 R15: ffff8880ba534d50 finish_lock_switch kernel/sched/sched.h:1346 [inline] finish_task_switch+0x178/0x610 kernel/sched/core.c:2678 context_switch kernel/sched/core.c:2814 [inline] __schedule+0x893/0x1de0 kernel/sched/core.c:3387 schedule+0x8d/0x1b0 kernel/sched/core.c:3431 freezable_schedule include/linux/freezer.h:172 [inline] futex_wait_queue_me+0x2e0/0x590 kernel/futex.c:2740 futex_wait+0x1b9/0x5a0 kernel/futex.c:2855 do_futex+0x1d8/0x1570 kernel/futex.c:3906 SYSC_futex kernel/futex.c:3966 [inline] SyS_futex+0x1da/0x290 kernel/futex.c:3934 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292 entry_SYSCALL_64_after_hwframe+0x46/0xbb RIP: 0033:0x4668c3 RSP: 002b:000000c00047db88 EFLAGS: 00000286 ORIG_RAX: 00000000000000ca RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000004668c3 RDX: 0000000000000000 RSI: 0000000000000080 RDI: 000000c000080950 RBP: 000000c00047dbd0 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000286 R12: 000000c00001e000 R13: 0000000000000001 R14: 000000c000083a00 R15: 0000000000000000