INFO: task blkid:20189 blocked for more than 120 seconds.
      Not tainted 4.9.83-gda9fb78 #40
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
blkid           D28272 20189   2224 0x00000006
 ffff8801b7f78000 ffff8801c38eb480 ffff8801c637ea00 ffff8801c2eb6000
 ffff8801db221b98 ffff8801b7fc76f8 ffffffff838a3e1b 0000000000000001
 0000000000000007 00ff8801b7f78000 ffff8801db222468 ffff8801db222490
Call Trace:
 [<ffffffff838a53bf>] schedule+0x7f/0x1b0 kernel/sched/core.c:3550
 [<ffffffff838a5d43>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3583
 [<ffffffff838ab352>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff838ab352>] mutex_lock_nested+0x312/0x870 kernel/locking/mutex.c:621
 [<ffffffff824b9b5f>] lo_release+0x1f/0x160 drivers/block/loop.c:1590
 [<ffffffff8162e317>] __blkdev_put+0x5f7/0x7e0 fs/block_dev.c:1598
 [<ffffffff8162f2d5>] blkdev_put+0x85/0x550 fs/block_dev.c:1663
 [<ffffffff8162f82b>] blkdev_close+0x8b/0xb0 fs/block_dev.c:1670
 [<ffffffff8157580c>] __fput+0x28c/0x6e0 fs/file_table.c:208
 [<ffffffff81575ce5>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff81195855>] task_work_run+0x115/0x190 kernel/task_work.c:116
 [<ffffffff8113c2c7>] exit_task_work include/linux/task_work.h:21 [inline]
 [<ffffffff8113c2c7>] do_exit+0x7e7/0x2a40 kernel/exit.c:833
 [<ffffffff811429d8>] do_group_exit+0x108/0x320 kernel/exit.c:937
 [<ffffffff81165854>] get_signal+0x4d4/0x14e0 kernel/signal.c:2317
 [<ffffffff81052c87>] do_signal+0x87/0x19f0 arch/x86/kernel/signal.c:807
 [<ffffffff81003a31>] exit_to_usermode_loop+0xe1/0x120 arch/x86/entry/common.c:157
 [<ffffffff810066cf>] prepare_exit_to_usermode arch/x86/entry/common.c:191 [inline]
 [<ffffffff810066cf>] syscall_return_slowpath arch/x86/entry/common.c:260 [inline]
 [<ffffffff810066cf>] do_syscall_64+0x36f/0x490 arch/x86/entry/common.c:287
 [<ffffffff838b4e7d>] entry_SYSCALL_64_after_swapgs+0x47/0xc5

Showing all locks held in the system:
2 locks held by khungtaskd/514:
 #0:  (rcu_read_lock){......}, at: [<ffffffff81373095>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff81373095>] watchdog+0x125/0xa70 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.?..}, at: [<ffffffff81238190>] debug_show_all_locks+0x70/0x280 kernel/locking/lockdep.c:4336
2 locks held by getty/3664:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838b3092>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff8200a5a4>] n_tty_read+0x1f4/0x16c0 drivers/tty/n_tty.c:2133
2 locks held by blkid/20189:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff8162dddc>] __blkdev_put+0xbc/0x7e0 fs/block_dev.c:1579
 #1:  (loop_index_mutex){+.+.+.}, at: [<ffffffff824b9b5f>] lo_release+0x1f/0x160 drivers/block/loop.c:1590
1 lock held by syz-executor2/23126:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff824b727f>] lo_ioctl+0x8f/0x1990 drivers/block/loop.c:1337
2 locks held by syz-executor4/23137:
 #0:  (loop_index_mutex){+.+.+.}, at: [<ffffffff824b973a>] loop_control_ioctl+0x7a/0x300 drivers/block/loop.c:1899
 #1:  (&lo->lo_ctl_mutex#2){+.+.+.}, at: [<ffffffff824b9836>] loop_control_ioctl+0x176/0x300 drivers/block/loop.c:1913

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

NMI backtrace for cpu 0
CPU: 0 PID: 514 Comm: khungtaskd Not tainted 4.9.83-gda9fb78 #40
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d86afd00 ffffffff81d95149 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810bb190 ffff8801d86afd38
 ffffffff81da026d 0000000000000000 0000000000000000 ffff8801b7f78418
Call Trace:
 [<ffffffff81d95149>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d95149>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81da026d>] nmi_cpu_backtrace+0xfd/0x120 lib/nmi_backtrace.c:99
 [<ffffffff81da03a7>] nmi_trigger_cpumask_backtrace+0x117/0x190 lib/nmi_backtrace.c:60
 [<ffffffff810bb284>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81373660>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81373660>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81373660>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81373660>] watchdog+0x6f0/0xa70 kernel/hung_task.c:239
 [<ffffffff8119a7bd>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838b500c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:361
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at pc 0xffffffff838b3b06