INFO: task syz-executor1:19600 blocked for more than 120 seconds.
      Not tainted 4.9.110-g00a0bcb #4
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor1   D29832 19600  19580 0x00000004
 ffff8801b76c1800 ffff8801a0d48000 ffff8801cb980000 ffff8801d8e61800
 ffff8801db221c18 ffff8801c498f8b8 ffffffff839e6ded ffff8801b76c20c8
 ffffed0036ed8418 ffff8801b76c1800 00fffc0000000000 ffff8801db2224e8
Call Trace:
 [<ffffffff839e83ef>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839e8d73>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3590
 [<ffffffff839ed1f6>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff839ed1f6>] mutex_lock_nested+0x326/0x870 kernel/locking/mutex.c:621
 [<ffffffff82123a8d>] flush_echoes drivers/tty/n_tty.c:799 [inline]
 [<ffffffff82123a8d>] __receive_buf drivers/tty/n_tty.c:1617 [inline]
 [<ffffffff82123a8d>] n_tty_receive_buf_common+0xcfd/0x2300 drivers/tty/n_tty.c:1711
 [<ffffffff82125100>] n_tty_receive_buf+0x30/0x40 drivers/tty/n_tty.c:1740
 [<ffffffff8211551f>] tiocsti drivers/tty/tty_io.c:2314 [inline]
 [<ffffffff8211551f>] tty_ioctl+0xc8f/0x2270 drivers/tty/tty_io.c:2905
 [<ffffffff815b2b9c>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815b2b9c>] file_ioctl fs/ioctl.c:493 [inline]
 [<ffffffff815b2b9c>] do_vfs_ioctl+0x1ac/0x11a0 fs/ioctl.c:677
 [<ffffffff815b3c1f>] SYSC_ioctl fs/ioctl.c:694 [inline]
 [<ffffffff815b3c1f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f7cd3>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb

Showing all locks held in the system:
2 locks held by khungtaskd/519:
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136662c>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136662c>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81425cb7>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3775:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f5e92>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8211e1e2>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2133
3 locks held by syz-executor1/19600:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f5e92>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&o_tty->termios_rwsem/1){++++..}, at: [<ffffffff82122e1b>] n_tty_receive_buf_common+0x8b/0x2300 drivers/tty/n_tty.c:1674
 #2:  (&ldata->output_lock){+.+...}, at: [<ffffffff82123a8d>] flush_echoes drivers/tty/n_tty.c:799 [inline]
 #2:  (&ldata->output_lock){+.+...}, at: [<ffffffff82123a8d>] __receive_buf drivers/tty/n_tty.c:1617 [inline]
 #2:  (&ldata->output_lock){+.+...}, at: [<ffffffff82123a8d>] n_tty_receive_buf_common+0xcfd/0x2300 drivers/tty/n_tty.c:1711

=============================================

NMI backtrace for cpu 0
CPU: 0 PID: 519 Comm: khungtaskd Not tainted 4.9.110-g00a0bcb #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d862fd08 ffffffff81eb2329 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b9580 ffff8801d862fd40
 ffffffff81ebd627 0000000000000000 0000000000000000 0000000000000002
Call Trace:
 [<ffffffff81eb2329>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb2329>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebd627>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebd5ba>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b9684>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81366bc4>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81366bc4>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81366bc4>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81366bc4>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119d04d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f7e9c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 13431 Comm: kworker/u4:1 Not tainted 4.9.110-g00a0bcb #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events_unbound flush_to_ldisc
c
task: ffff8801a029e000 task.stack: ffff8801d88d8000
RIP: 0010:[<ffffffff8135e940>] 
c [<ffffffff8135e940>] __sanitizer_cov_trace_pc+0x0/0x50
RSP: 0018:ffff8801d88df990  EFLAGS: 00000293
RAX: ffff8801a029e000 RBX: ffffc90000400000 RCX: 0000000000000001
RDX: 0000000000000000 RSI: ffffffff8211a10e RDI: ffffc90000401952
RBP: ffff8801d88dfa00 R08: ffff8801a029e9b0 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 000000098deb26f3
R13: 0000000000002b80 R14: dffffc0000000000 R15: 000000098deb26f3
FS:  0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fecc3818140 CR3: 00000001b81c1000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff8211a078
c ffffffff839f0941
c ffffc90000402308
c ffffc90000402278
c
 ffffed003b2ef5c5
c ffff8801d977ae2c
c ffffc90000400020
c 00000001000015ff
c
 ffff8801d977aa80
c ffffc90000400000
c ffff8801d977aa80
c 0000000000002b80
c
Call Trace:
 [<ffffffff8211b9d7>] commit_echoes+0x147/0x1b0 drivers/tty/n_tty.c:766
 [<ffffffff8212349a>] n_tty_receive_char_inline drivers/tty/n_tty.c:1390 [inline]
 [<ffffffff8212349a>] n_tty_receive_buf_standard drivers/tty/n_tty.c:1552 [inline]
 [<ffffffff8212349a>] __receive_buf drivers/tty/n_tty.c:1615 [inline]
 [<ffffffff8212349a>] n_tty_receive_buf_common+0x70a/0x2300 drivers/tty/n_tty.c:1711
 [<ffffffff821250c3>] n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1746
 [<ffffffff8212abbf>] tty_ldisc_receive_buf+0xaf/0x190 drivers/tty/tty_buffer.c:455
 [<ffffffff8212bbc3>] receive_buf drivers/tty/tty_buffer.c:474 [inline]
 [<ffffffff8212bbc3>] flush_to_ldisc+0x253/0x370 drivers/tty/tty_buffer.c:533
 [<ffffffff8118d121>] process_one_work+0x7e1/0x1500 kernel/workqueue.c:2092
 [<ffffffff8118df16>] worker_thread+0xd6/0x10a0 kernel/workqueue.c:2226
 [<ffffffff8119d04d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f7e9c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Code: 
c1d 
c00 
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c48 
c89 
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cd1 
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c00 
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cff 
cff 
c66 
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c0f 
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c84 
c00 
c00 
c00 
c00 
c00 
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c1f 
c00 
c<55> 
c48 
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c65 
c48 
c8b 
c04 
c25 
cc0 
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c01 
c00 
c65 
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c15 
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c93 
ccb 
c7e 
c81 
c