INFO: task loop0:3912 blocked for more than 120 seconds.
      Not tainted 4.9.109-ge1815b3 #52
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
loop0           D27080  3912      2 0x00000000
 ffff8801d4ce8000 ffff8801d6eb7480 ffff8801d6eb7480 ffff8801d4cec800
 ffff8801db321c18 ffff8801d5376df0 ffffffff839e8a8d 0000000041b58ab3
 ffffffff843c2288 ffffffff81236160 0000000000000000 ffff8801db3224e8
Call Trace:
 [<ffffffff839ea08f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839f64a1>] schedule_timeout+0x861/0xf70 kernel/time/timer.c:1768
 [<ffffffff839e826a>] io_schedule_timeout+0x1ba/0x390 kernel/sched/core.c:5180
 [<ffffffff81e51f0c>] io_schedule include/linux/sched.h:460 [inline]
 [<ffffffff81e51f0c>] bt_get.isra.8+0x27c/0x780 block/blk-mq-tag.c:141
 [<ffffffff81e52e1c>] __blk_mq_get_tag block/blk-mq-tag.c:163 [inline]
 [<ffffffff81e52e1c>] blk_mq_get_tag+0xac/0x220 block/blk-mq-tag.c:192
 [<ffffffff81e4254a>] __blk_mq_alloc_request+0x2a/0xaa0 block/blk-mq.c:196
 [<ffffffff81e4494b>] blk_mq_map_request.isra.38+0x3ab/0x900 block/blk-mq.c:1207
 [<ffffffff81e4cd96>] blk_sq_make_request+0x1d6/0x1220 block/blk-mq.c:1374
 [<ffffffff81e1fcce>] generic_make_request+0x20e/0x9b0 block/blk-core.c:2055
 [<ffffffff81e20520>] submit_bio+0xb0/0x460 block/blk-core.c:2126
 [<ffffffff8164390a>] dio_bio_submit fs/direct-io.c:420 [inline]
 [<ffffffff8164390a>] do_blockdev_direct_IO+0x35da/0x5a80 fs/direct-io.c:1301
 [<ffffffff81645e55>] __blockdev_direct_IO+0xa5/0xd0 fs/direct-io.c:1360
 [<ffffffff8162fa00>] blkdev_direct_IO+0xa0/0xd0 fs/block_dev.c:183
 [<ffffffff8143e740>] generic_file_read_iter+0x660/0x1a90 mm/filemap.c:1951
 [<ffffffff81632605>] blkdev_read_iter+0x105/0x170 fs/block_dev.c:1738
 [<ffffffff825cdf13>] lo_rw_aio+0x6b3/0x8a0 drivers/block/loop.c:506
 [<ffffffff825ce4d7>] do_req_filebacked drivers/block/loop.c:543 [inline]
 [<ffffffff825ce4d7>] loop_handle_cmd drivers/block/loop.c:1698 [inline]
 [<ffffffff825ce4d7>] loop_queue_work+0x3d7/0x2320 drivers/block/loop.c:1710
 [<ffffffff8119d429>] kthread_worker_fn+0x249/0x6b0 kernel/kthread.c:627
 [<ffffffff8119d04d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f9b5c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373

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: [<ffffffff839f7b32>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8211fce2>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2133

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

NMI backtrace for cpu 0
CPU: 0 PID: 519 Comm: khungtaskd Not tainted 4.9.109-ge1815b3 #52
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d84dfd08 ffffffff81eb3e29 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b9580 ffff8801d84dfd40
 ffffffff81ebf127 0000000000000000 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb3e29>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb3e29>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebf127>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebf0ba>] 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
 [<ffffffff839f9b5c>] 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: 3909 Comm: sshd Not tainted 4.9.109-ge1815b3 #52
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d4cec800 task.stack: ffff8801d50b8000
RIP: 0010:[<ffffffff839f9f78>] 
c [<ffffffff839f9f78>] irq_entries_start+0x408/0x690 arch/x86/entry/entry_64.S:395
RSP: 0018:ffff8801d50bf438  EFLAGS: 00000082
RAX: 0000000000000007 RBX: 0000000000000282 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000282
RBP: ffff8801d50bf470 R08: 0000000000000092 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801db31c900
R13: 74732d0064687373 R14: 006d6561642d706f R15: ffff8801d50bf5d8
FS:  00007ff6b27fd7c0(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f79ea486000 CR3: 00000001d7b1c000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff839f908f
c 0000000000000010
c 0000000000000282
c ffff8801d50bf460
c
 0000000000000018
c ffff8801db31c900
c ffff8801db31c9c0
c ffff8801d50bf598
c
 ffffffff812a3400
c ffff8801d50bf490
c 1ffff1003aa17e9a
c 00000000000000c0
c
Call Trace:
 [<ffffffff812a3400>] unlock_hrtimer_base kernel/time/hrtimer.c:803 [inline]
 [<ffffffff812a3400>] hrtimer_start_range_ns+0x670/0x1380 kernel/time/hrtimer.c:1010
 [<ffffffff839f75f3>] hrtimer_start_expires include/linux/hrtimer.h:407 [inline]
 [<ffffffff839f75f3>] schedule_hrtimeout_range_clock+0x163/0x330 kernel/time/hrtimer.c:1732
 [<ffffffff839f77ea>] schedule_hrtimeout_range+0x2a/0x40 kernel/time/hrtimer.c:1776
 [<ffffffff815b5aff>] poll_schedule_timeout+0x10f/0x200 fs/select.c:242
 [<ffffffff815b761f>] do_select+0x100f/0x13b0 fs/select.c:534
 [<ffffffff815b7eac>] core_sys_select+0x4ec/0x750 fs/select.c:611
 [<ffffffff815b8268>] SYSC_select fs/select.c:652 [inline]
 [<ffffffff815b8268>] SyS_select+0x158/0x1e0 fs/select.c:634
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f9993>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 
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c