Buffer I/O error on dev loop0, logical block 0, async page read
INFO: task blkid:21204 blocked for more than 120 seconds.
      Not tainted 4.9.94-g8683408 #3
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
blkid           D27064 21204   6618 0x00000006
 ffff8801c70d3000 0000000000000000 ffff8801ba6c64c0 ffff8801d9b73000
 ffff8801db321b98 ffff8801c2e9f310 ffffffff838c040d 0000000041b58ab3
 ffffffff841a49d8 ffffffff81234350 00ff8801c2e9f4e8 ffff8801db322468
Call Trace:
 [<ffffffff838c1a0f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff838cde21>] schedule_timeout+0x861/0xf70 kernel/time/timer.c:1768
 [<ffffffff838bfbea>] io_schedule_timeout+0x1ba/0x390 kernel/sched/core.c:5180
 [<ffffffff838c2e59>] io_schedule include/linux/sched.h:460 [inline]
 [<ffffffff838c2e59>] bit_wait_io+0x19/0xa0 kernel/sched/wait.c:582
 [<ffffffff838c26fe>] __wait_on_bit_lock+0xce/0x1c0 kernel/sched/wait.c:421
 [<ffffffff8143240f>] __lock_page+0xff/0x160 mm/filemap.c:934
 [<ffffffff814695b8>] lock_page include/linux/pagemap.h:454 [inline]
 [<ffffffff814695b8>] truncate_inode_pages_range+0x818/0x1290 mm/truncate.c:373
 [<ffffffff8146a054>] truncate_inode_pages+0x24/0x30 mm/truncate.c:401
 [<ffffffff8162be4c>] kill_bdev+0xbc/0xf0 fs/block_dev.c:96
 [<ffffffff8162e193>] __blkdev_put+0x1e3/0x840 fs/block_dev.c:1586
 [<ffffffff8162f5d5>] blkdev_put+0x85/0x560 fs/block_dev.c:1663
 [<ffffffff8162fb3b>] blkdev_close+0x8b/0xb0 fs/block_dev.c:1670
 [<ffffffff815759d3>] __fput+0x263/0x700 fs/file_table.c:208
 [<ffffffff81575ef5>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8119600c>] task_work_run+0x10c/0x180 kernel/task_work.c:116
 [<ffffffff8113ec91>] exit_task_work include/linux/task_work.h:21 [inline]
 [<ffffffff8113ec91>] do_exit+0x9e1/0x27c0 kernel/exit.c:837
 [<ffffffff81144d91>] do_group_exit+0x111/0x340 kernel/exit.c:941
 [<ffffffff81167b5f>] get_signal+0x4cf/0x1450 kernel/signal.c:2317
 [<ffffffff810524d7>] do_signal+0x87/0x19f0 arch/x86/kernel/signal.c:807
 [<ffffffff81005581>] exit_to_usermode_loop+0xe1/0x120 arch/x86/entry/common.c:157
 [<ffffffff810064d4>] prepare_exit_to_usermode arch/x86/entry/common.c:191 [inline]
 [<ffffffff810064d4>] syscall_return_slowpath arch/x86/entry/common.c:260 [inline]
 [<ffffffff810064d4>] do_syscall_64+0x364/0x490 arch/x86/entry/common.c:287
 [<ffffffff838d1313>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb

Showing all locks held in the system:
2 locks held by khungtaskd/515:
 #0:  (rcu_read_lock){......}, at: [<ffffffff813646bc>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff813646bc>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81423bb0>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
1 lock held by rsyslogd/3642:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<ffffffff815d565c>] __fdget_pos+0xac/0xd0 fs/file.c:781
2 locks held by getty/3738:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838cf4b2>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff82007082>] n_tty_read+0x202/0x16b0 drivers/tty/n_tty.c:2133
1 lock held by blkid/21204:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff8162e06b>] __blkdev_put+0xbb/0x840 fs/block_dev.c:1579
1 lock held by blkid/21367:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff8162e06b>] __blkdev_put+0xbb/0x840 fs/block_dev.c:1579

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

NMI backtrace for cpu 0
CPU: 0 PID: 515 Comm: khungtaskd Not tainted 4.9.94-g8683408 #3
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d867fd08 ffffffff81d9b509 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b7d60 ffff8801d867fd40
 ffffffff81da6837 0000000000000000 0000000000000000 0000000000000002
Call Trace:
 [<ffffffff81d9b509>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d9b509>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81da6837>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81da67ca>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b7e64>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81364c54>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81364c54>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81364c54>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81364c54>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119ad2d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838d14dc>] 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: 7 Comm: rcu_preempt Not tainted 4.9.94-g8683408 #3
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d9b41800 task.stack: ffff8801d9b50000
RIP: 0010:[<ffffffff811ecbfa>] 
c [<ffffffff811ecbfa>] __dequeue_entity kernel/sched/fair.c:590 [inline]
RIP: 0010:[<ffffffff811ecbfa>] 
c [<ffffffff811ecbfa>] set_next_entity+0x3ba/0xbf0 kernel/sched/fair.c:3818
RSP: 0018:ffff8801d9b578a0  EFLAGS: 00000046
RAX: 0000000000000000 RBX: ffff8801b9b11880 RCX: ffff8801db321c50
RDX: dffffc0000000000 RSI: 1ffff1003b66438a RDI: ffff8801b9b11898
RBP: ffff8801d9b578f0 R08: ffff8801db321ce8 R09: 0000000000006000
R10: ffff8801d9b41a70 R11: 0000000000000000 R12: ffffffff84c6d380
R13: ffffffff84651400 R14: ffff8801b9b11890 R15: ffff8801db321c20
FS:  0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fec12858000 CR3: 00000001bc8e6000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 0000000000000000
c ffff8801d9b578f0
c ffffffff811e3597
c ffff8801db321ce8
c
 ffff8801db321c50
c ffff8801d9b41880
c dffffc0000000000
c ffff8801b9b11800
c
 ffff8801b9b11880
c ffff8801db321b80
c ffff8801d9b57a10
c ffffffff81204a88
c
Call Trace:
 [<ffffffff81204a88>] pick_next_task_fair+0x1118/0x1e30 kernel/sched/fair.c:7544
 [<ffffffff838c004a>] pick_next_task kernel/sched/core.c:3362 [inline]
 [<ffffffff838c004a>] __schedule+0x28a/0x1bd0 kernel/sched/core.c:3484
 [<ffffffff838c1a0f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff838cda4b>] schedule_timeout+0x48b/0xf70 kernel/time/timer.c:1791
 [<ffffffff8128735d>] rcu_gp_kthread+0xb9d/0x2110 kernel/rcu/tree.c:2227
 [<ffffffff8119ad2d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838d14dc>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Code: 
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c