INFO: task blkid:2437 blocked for more than 140 seconds.
      Not tainted 4.4.174+ #4
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
blkid           D ffff8801d0fbfaf8 29232  2437    583 0x00000004
 ffff8801d0fbfaf8 ffff8800b41c4740 4db4746c4ba3be89 ffff8800b41c4740
 0000000000000002 ffff8800b41c5000 ffff8801db61f180 ffff8801db61f1a8
 ffff8801db61e898 ffffffff82e151c0 ffff8800b41c4740 ffffed003a1f7001
Call Trace:
 [<ffffffff82709b79>] schedule+0x99/0x1d0 kernel/sched/core.c:3355
 [<ffffffff8270a333>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3388
 [<ffffffff8270c492>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff8270c492>] mutex_lock_nested+0x3c2/0xb80 kernel/locking/mutex.c:621
 [<ffffffff81d48124>] __lo_release drivers/block/loop.c:1653 [inline]
 [<ffffffff81d48124>] lo_release+0x84/0x1b0 drivers/block/loop.c:1676
 [<ffffffff8154e4e1>] __blkdev_put+0x461/0x840 fs/block_dev.c:1535
 [<ffffffff8154f738>] blkdev_put+0x88/0x560 fs/block_dev.c:1600
 [<ffffffff8154fc9b>] blkdev_close+0x8b/0xb0 fs/block_dev.c:1607
 [<ffffffff8149c8c6>] __fput+0x246/0x710 fs/file_table.c:208
 [<ffffffff8149ce16>] ____fput+0x16/0x20 fs/file_table.c:244
 [<ffffffff8112f352>] task_work_run+0x202/0x2b0 kernel/task_work.c:115
 [<ffffffff81003dca>] tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 [<ffffffff81003dca>] exit_to_usermode_loop+0x14a/0x170 arch/x86/entry/common.c:188
 [<ffffffff8100569b>] prepare_exit_to_usermode arch/x86/entry/common.c:221 [inline]
 [<ffffffff8100569b>] syscall_return_slowpath+0x25b/0x2e0 arch/x86/entry/common.c:286
 [<ffffffff82718ce1>] int_ret_from_sys_call+0x25/0xa3
3 locks held by blkid/2437:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff8154e13b>] __blkdev_put+0xbb/0x840 fs/block_dev.c:1516
 #1:  (loop_index_mutex){+.+.+.}, at: [<ffffffff81d480be>] lo_release+0x1e/0x1b0 drivers/block/loop.c:1675
 #2:  (loop_ctl_mutex#2){+.+.+.}, at: [<ffffffff81d48124>] __lo_release drivers/block/loop.c:1653 [inline]
 #2:  (loop_ctl_mutex#2){+.+.+.}, at: [<ffffffff81d48124>] lo_release+0x84/0x1b0 drivers/block/loop.c:1676
Sending NMI to all CPUs:
NMI backtrace for cpu 0
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.4.174+ #4
task: ffffffff82e151c0 task.stack: ffffffff82e00000
RIP: 0010:[<ffffffff810a1dc2>]  [<ffffffff810a1dc2>] native_safe_halt+0x2/0x10 arch/x86/include/asm/irqflags.h:53
RSP: 0018:ffffffff82e07db0  EFLAGS: 00000246
RAX: 0000000000000007 RBX: ffffffff8319bf68 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffff82e15a84
RBP: ffffffff82e07de0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffffffff82e08000 R14: dffffc0000000000 R15: ffffffff82e00000
FS:  0000000000000000(0000) GS:ffff8801db600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f9f476a4000 CR3: 00000001d70a5000 CR4: 00000000001606b0
Stack:
 ffffffff81020b16 ffffffff82e00000 0000000000000000 ffffffff82e08000
 dffffc0000000000 ffffffff82e00000 ffffffff82e07df0 ffffffff81022d50
 ffffffff82e07e08 ffffffff811eb4c8 0000000000000000 ffffffff82e07ed0
Call Trace:
 [<ffffffff81022d50>] arch_cpu_idle+0x10/0x20 arch/x86/kernel/process.c:423
 [<ffffffff811eb4c8>] default_idle_call+0x48/0x70 kernel/sched/idle.c:93
 [<ffffffff811ebca1>] cpuidle_idle_call kernel/sched/idle.c:157 [inline]
 [<ffffffff811ebca1>] cpu_idle_loop kernel/sched/idle.c:253 [inline]
 [<ffffffff811ebca1>] cpu_startup_entry+0x6d1/0x810 kernel/sched/idle.c:301
 [<ffffffff827055f9>] rest_init+0x190/0x199 init/main.c:410
 [<ffffffff831d58a0>] start_kernel+0x64a/0x67e init/main.c:682
 [<ffffffff831d430a>] x86_64_start_reservations+0x29/0x2b arch/x86/kernel/head64.c:196
 [<ffffffff831d4443>] x86_64_start_kernel+0x137/0x15a arch/x86/kernel/head64.c:185
Code: 2e 0f 1f 84 00 00 00 00 00 fa c3 0f 1f 40 00 66 2e 0f 1f 84 00 00 00 00 00 fb c3 0f 1f 40 00 66 2e 0f 1f 84 00 00 00 00 00 fb f4 <c3> 0f 1f 00 66 2e 0f 1f 84 00 00 00 00 00 f4 c3 0f 1f 40 00 66 
NMI backtrace for cpu 1
CPU: 1 PID: 20 Comm: khungtaskd Not tainted 4.4.174+ #4
task: ffff8801da6f4740 task.stack: ffff8800001d0000
RIP: 0010:[<ffffffff8109b617>]  [<ffffffff8109b617>] _flat_send_IPI_mask arch/x86/kernel/apic/apic_flat_64.c:62 [inline]
RIP: 0010:[<ffffffff8109b617>]  [<ffffffff8109b617>] flat_send_IPI_mask+0xf7/0x1b0 arch/x86/kernel/apic/apic_flat_64.c:69
RSP: 0018:ffff8800001d7c88  EFLAGS: 00000046
RAX: 0000000000000000 RBX: 0000000000000c00 RCX: 0000000000000000
RDX: 0000000000000c00 RSI: 0000000000000000 RDI: ffffffffff5fc300
RBP: ffff8800001d7cb8 R08: 0000000000000018 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000001 R12: 0000000000000246
R13: 0000000003000000 R14: ffffffff82e5f2e0 R15: 0000000000000002
FS:  0000000000000000(0000) GS:ffff8801db700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000163e308 CR3: 00000000b5243000 CR4: 00000000001606b0
Stack:
 0000000000000001 ffffffff82e5f2e0 ffffffff831a6ac0 fffffbfff0634c34
 000000000001b6c0 0000000000000008 ffff8800001d7cd8 ffffffff81092bee
 0000000000000008 ffffffff82924260 ffff8800001d7d30 ffffffff81ab8252
Call Trace:
 [<ffffffff81092bee>] nmi_raise_cpu_backtrace+0x5e/0x80 arch/x86/kernel/apic/hw_nmi.c:33
 [<ffffffff81ab8252>] nmi_trigger_all_cpu_backtrace.cold+0xa1/0xae lib/nmi_backtrace.c:85
 [<ffffffff81092ca4>] arch_trigger_all_cpu_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
 [<ffffffff813b4762>] trigger_all_cpu_backtrace include/linux/nmi.h:44 [inline]
 [<ffffffff813b4762>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff813b4762>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff813b4762>] watchdog.cold+0xd3/0xee kernel/hung_task.c:238
 [<ffffffff811342c3>] kthread+0x273/0x310 kernel/kthread.c:211
 [<ffffffff82718fc5>] ret_from_fork+0x55/0x80 arch/x86/entry/entry_64.S:537
Code: 00 c3 5f ff 80 e6 10 75 e1 41 c1 e5 18 44 89 2c 25 10 c3 5f ff 44 89 fa 09 da 80 cf 04 41 83 ff 02 0f 44 d3 89 14 25 00 c3 5f ff <41> f7 c4 00 02 00 00 75 1e 4c 89 e7 57 9d 0f 1f 44 00 00 e8 f1