INFO: task syz-executor738:4050 blocked for more than 120 seconds.
      Not tainted 4.9.98-g0e25e2c #15
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor738 D29832  4050   3867 0x00000004
 ffff8801d7203000 0000000000000000 ffff8801d7584a80 ffff8801d9bc9800
 ffff8801db321b98 ffff8801d71078b8 ffffffff839e375d ffff8801d72038c8
 ffffed003ae40718 ffff8801d7203000 00fffc0000000000 ffff8801db322468
Call Trace:
 [<ffffffff839e4d5f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839e56e3>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3590
 [<ffffffff839e9b66>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff839e9b66>] mutex_lock_nested+0x326/0x870 kernel/locking/mutex.c:621
 [<ffffffff8212259d>] flush_echoes drivers/tty/n_tty.c:799 [inline]
 [<ffffffff8212259d>] __receive_buf drivers/tty/n_tty.c:1617 [inline]
 [<ffffffff8212259d>] n_tty_receive_buf_common+0xcfd/0x2300 drivers/tty/n_tty.c:1711
 [<ffffffff82123c10>] n_tty_receive_buf+0x30/0x40 drivers/tty/n_tty.c:1740
 [<ffffffff8211402f>] tiocsti drivers/tty/tty_io.c:2314 [inline]
 [<ffffffff8211402f>] tty_ioctl+0xc8f/0x2270 drivers/tty/tty_io.c:2905
 [<ffffffff815b051c>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815b051c>] file_ioctl fs/ioctl.c:493 [inline]
 [<ffffffff815b051c>] do_vfs_ioctl+0x1ac/0x11a0 fs/ioctl.c:677
 [<ffffffff815b159f>] SYSC_ioctl fs/ioctl.c:694 [inline]
 [<ffffffff815b159f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f4653>] 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: [<ffffffff813646ec>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff813646ec>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81423ce0>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3777:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f2802>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8211ccf2>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2133
3 locks held by syz-executor738/4050:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f2802>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&o_tty->termios_rwsem/1){++++..}, at: [<ffffffff8212192b>] n_tty_receive_buf_common+0x8b/0x2300 drivers/tty/n_tty.c:1674
 #2:  (&ldata->output_lock){+.+...}, at: [<ffffffff8212259d>] flush_echoes drivers/tty/n_tty.c:799 [inline]
 #2:  (&ldata->output_lock){+.+...}, at: [<ffffffff8212259d>] __receive_buf drivers/tty/n_tty.c:1617 [inline]
 #2:  (&ldata->output_lock){+.+...}, at: [<ffffffff8212259d>] 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 4.9.98-g0e25e2c #15
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d85dfd08 ffffffff81eb0fc9 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b7da0 ffff8801d85dfd40
 ffffffff81ebc2c7 0000000000000000 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb0fc9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb0fc9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebc2c7>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebc25a>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b7ea4>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81364c84>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81364c84>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81364c84>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81364c84>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119ad5d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f481c>] 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: 3876 Comm: kworker/u4:3 Not tainted 4.9.98-g0e25e2c #15
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events_unbound flush_to_ldisc
c
task: ffff8801d8158000 task.stack: ffff8801b5f60000
RIP: 0010:[<ffffffff8135ca1a>] 
c [<ffffffff8135ca1a>] check_kcov_mode kernel/kcov.c:66 [inline]
RIP: 0010:[<ffffffff8135ca1a>] 
c [<ffffffff8135ca1a>] __sanitizer_cov_trace_pc+0x1a/0x50 kernel/kcov.c:100
RSP: 0018:ffff8801b5f679c8  EFLAGS: 00000246
RAX: ffff8801d8158000 RBX: ffffc90001033000 RCX: 0000000000000006
RDX: 0000000000000000 RSI: ffffffff82118b88 RDI: ffffc90001034f1f
RBP: ffff8801b5f679c8 R08: ffff8801d81589b0 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 000000097e254cc0
R13: 000000000000310e R14: dffffc0000000000 R15: 000000097e254cc0
FS:  0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fa603817000 CR3: 00000001cd8d7000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff8801b5f67a40
c ffffffff82118b9f
c ffff8801b5f67a18
c 0000000000000000
c
 ffffc90001035278
c ffffed003ae338f5
c ffff8801d719c7ac
c ffffc90001033020
c
 0000000000000900
c ffff8801d719c400
c ffffc90001035300
c ffffc90001033000
c
Call Trace:
 [<ffffffff82118b9f>] echo_buf drivers/tty/n_tty.c:146 [inline]
 [<ffffffff82118b9f>] __process_echoes+0x5cf/0x780 drivers/tty/n_tty.c:734
 [<ffffffff821225d4>] flush_echoes drivers/tty/n_tty.c:801 [inline]
 [<ffffffff821225d4>] __receive_buf drivers/tty/n_tty.c:1617 [inline]
 [<ffffffff821225d4>] n_tty_receive_buf_common+0xd34/0x2300 drivers/tty/n_tty.c:1711
 [<ffffffff82123bd3>] n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1746
 [<ffffffff821296cf>] tty_ldisc_receive_buf+0xaf/0x190 drivers/tty/tty_buffer.c:455
 [<ffffffff8212a6d3>] receive_buf drivers/tty/tty_buffer.c:474 [inline]
 [<ffffffff8212a6d3>] flush_to_ldisc+0x253/0x370 drivers/tty/tty_buffer.c:533
 [<ffffffff8118ae31>] process_one_work+0x7e1/0x1500 kernel/workqueue.c:2092
 [<ffffffff8118bc26>] worker_thread+0xd6/0x10a0 kernel/workqueue.c:2226
 [<ffffffff8119ad5d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f481c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Code: 
cf9 
cfe 
cff 
cff 
c66 
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c84 
c00 
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c00 
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c48 
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c65 
c48 
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c01 
c00 
c65 
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c15 
cbc 
cb2 
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c7e 
c81 
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c00 
c01 
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c00 
c<48> 
c8b 
c75 
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c75 
c2b 
c8b 
c90 
c80 
c12 
c00 
c00 
c83 
cfa 
c02 
c75 
c20 
c48 
c8b 
c88 
c88 
c