INFO: task hung in n_tty

Kernel	Title	Rank 🛈	Repro	Fix bisect	Count	Last	Reported	Patched	Status
linux-4.19	INFO: task hung in n_tty_poll	1	C	error	4	1249d	1641d	0/1	upstream: reported C repro on 2021/05/13 07:45
linux-4.14	INFO: task hung in n_tty_poll (2)	1	C	error	1	1162d	1252d	0/1	upstream: reported C repro on 2022/06/06 01:17
upstream	INFO: task hung in n_tty_poll kernel	1			1	104d	104d	0/29	auto-obsoleted due to no activity on 2025/10/26 03:54

Bluetooth: hci2 command 0x0406 tx timeout INFO: task syz-executor.1:10267 blocked for more than 140 seconds. Not tainted 4.14.228-syzkaller #0 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. syz-executor.1 D28456 10267 7981 0x00000004 Call Trace: context_switch kernel/sched/core.c:2808 [inline] __schedule+0x88b/0x1de0 kernel/sched/core.c:3384 schedule+0x8d/0x1b0 kernel/sched/core.c:3428 schedule_timeout+0x80a/0xe90 kernel/time/timer.c:1724 do_wait_for_common kernel/sched/completion.c:91 [inline] __wait_for_common kernel/sched/completion.c:112 [inline] wait_for_common+0x272/0x430 kernel/sched/completion.c:123 flush_work+0x3fe/0x770 kernel/workqueue.c:2893 n_tty_poll+0x4de/0x7d0 drivers/tty/n_tty.c:2412 tty_poll+0x129/0x1a0 drivers/tty/tty_io.c:2102 do_select+0xa83/0x1290 fs/select.c:513 core_sys_select+0x32f/0x6a0 fs/select.c:656 do_pselect fs/select.c:733 [inline] SYSC_pselect6 fs/select.c:774 [inline] SyS_pselect6+0x358/0x3c0 fs/select.c:759 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292 entry_SYSCALL_64_after_hwframe+0x46/0xbb RIP: 0033:0x466459 RSP: 002b:00007f5c5f193188 EFLAGS: 00000246 ORIG_RAX: 000000000000010e RAX: ffffffffffffffda RBX: 000000000056bf60 RCX: 0000000000466459 RDX: 0000000000000000 RSI: 00000000200000c0 RDI: 0000000000000040 RBP: 00000000004bf9fb R08: 0000000000000000 R09: 0000000000000000 R10: 0000000020000140 R11: 0000000000000246 R12: 000000000056bf60 R13: 00007ffd9ebc125f R14: 00007f5c5f193300 R15: 0000000000022000 Showing all locks held in the system: 1 lock held by khungtaskd/1532: #0: (tasklist_lock){.+.+}, at: [<ffffffff87003f47>] debug_show_all_locks+0x7c/0x21a kernel/locking/lockdep.c:4548 1 lock held by in:imklog/7686: #0: (&f->f_pos_lock){+.+.}, at: [<ffffffff818d129b>] __fdget_pos+0x1fb/0x2b0 fs/file.c:769 1 lock held by syz-executor.1/10267: #0: (&tty->ldisc_sem){++++}, at: [<ffffffff83547072>] tty_ldisc_ref_wait+0x22/0x80 drivers/tty/tty_ldisc.c:284 ============================================= NMI backtrace for cpu 1 CPU: 1 PID: 1532 Comm: khungtaskd Not tainted 4.14.228-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+0x1b2/0x281 lib/dump_stack.c:58 nmi_cpu_backtrace.cold+0x57/0x93 lib/nmi_backtrace.c:101 nmi_trigger_cpumask_backtrace+0x13a/0x180 lib/nmi_backtrace.c:62 trigger_all_cpu_backtrace include/linux/nmi.h:140 [inline] check_hung_uninterruptible_tasks kernel/hung_task.c:195 [inline] watchdog+0x5b9/0xb40 kernel/hung_task.c:274 kthread+0x30d/0x420 kernel/kthread.c:232 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404 Sending NMI from CPU 1 to CPUs 0: NMI backtrace for cpu 0 CPU: 0 PID: 22 Comm: kworker/u4:1 Not tainted 4.14.228-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Workqueue: events_unbound flush_to_ldisc task: ffff8880b55ec5c0 task.stack: ffff8880b55f8000 RIP: 0010:__lock_release kernel/locking/lockdep.c:3760 [inline] RIP: 0010:lock_release+0x21e/0x870 kernel/locking/lockdep.c:4017 RSP: 0018:ffff8880b55ff828 EFLAGS: 00000006 RAX: 0000000000000009 RBX: 1ffff11016abff08 RCX: 1ffffffff127a2e4 RDX: 0000000000000004 RSI: 0000000000000002 RDI: ffff8880b55ece44 RBP: ffff8880ba42a318 R08: ffff8880ba42ac30 R09: 0000000000000001 R10: 0000000000000000 R11: ffff8880b55ec5c0 R12: ffffffff8139b8ec R13: ffffffff8beb9d40 R14: ffff8880b55ec5c0 R15: 0000000000000009 FS: 0000000000000000(0000) GS:ffff8880ba400000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000000c02160d2a0 CR3: 00000000b0110000 CR4: 00000000001406f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: __raw_spin_unlock include/linux/spinlock_api_smp.h:150 [inline] _raw_spin_unlock+0x17/0x40 kernel/locking/spinlock.c:184 rq_unlock kernel/sched/sched.h:1774 [inline] ttwu_queue kernel/sched/core.c:1875 [inline] try_to_wake_up+0x6ec/0x1100 kernel/sched/core.c:2087 wake_up_worker kernel/workqueue.c:840 [inline] insert_work+0x226/0x2c0 kernel/workqueue.c:1313 __queue_work+0x4f3/0xf70 kernel/workqueue.c:1465 queue_work_on+0x159/0x1d0 kernel/workqueue.c:1490 pty_write+0x172/0x1d0 drivers/tty/pty.c:126 tty_put_char+0xfe/0x120 drivers/tty/tty_io.c:2885 __process_echoes+0x48c/0x8c0 drivers/tty/n_tty.c:728 flush_echoes drivers/tty/n_tty.c:829 [inline] __receive_buf drivers/tty/n_tty.c:1648 [inline] n_tty_receive_buf_common+0x9a3/0x25a0 drivers/tty/n_tty.c:1742 tty_ldisc_receive_buf+0x9e/0x170 drivers/tty/tty_buffer.c:455 tty_port_default_receive_buf+0x6e/0xa0 drivers/tty/tty_port.c:37 receive_buf drivers/tty/tty_buffer.c:475 [inline] flush_to_ldisc+0x1dd/0x3f0 drivers/tty/tty_buffer.c:527 process_one_work+0x793/0x14a0 kernel/workqueue.c:2116 worker_thread+0x5cc/0xff0 kernel/workqueue.c:2250 kthread+0x30d/0x420 kernel/kthread.c:232 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404 Code: ff df 4c 89 ea 48 c1 ea 03 0f b6 14 02 4c 89 e8 83 e0 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 46 05 00 00 44 89 f8 0b 05 92 e6 a9 0a <0f> 84 3e 04 00 00 44 89 fa 48 89 ee 4c 89 f7 48 8d 4c 24 38 e8