unregister_netdevice: waiting for lo to become free. Usage count = 1
INFO: task syz-executor2:3786 blocked for more than 120 seconds.
      Not tainted 4.9.66-g87cdf4e #104
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor2   D29680  3786  26570 0x00000004
 ffff8801a94f8000 ffff8801ca505500 ffff8801ca505f80 ffff8801c7d6e000
 ffff8801db221418 ffff8801a88efa40 ffffffff838981cb 0000000000000002
 0000000041b58ab3 00ffffff8418717c ffff8801db221ce8 ffff8801db221d10
Call Trace:
 [<ffffffff8389976f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3550
unregister_netdevice: waiting for lo to become free. Usage count = 1
 [<ffffffff81d1db54>] blk_mq_freeze_queue_wait+0x114/0x230 block/blk-mq.c:75
 [<ffffffff81d26bed>] blk_freeze_queue block/blk-mq.c:92 [inline]
 [<ffffffff81d26bed>] blk_mq_freeze_queue+0x1d/0x20 block/blk-mq.c:101
 [<ffffffff824af85f>] loop_switch drivers/block/loop.c:599 [inline]
 [<ffffffff824af85f>] loop_change_fd drivers/block/loop.c:682 [inline]
 [<ffffffff824af85f>] lo_ioctl+0xfdf/0x1990 drivers/block/loop.c:1343
 [<ffffffff81d338ba>] __blkdev_driver_ioctl block/ioctl.c:294 [inline]
 [<ffffffff81d338ba>] blkdev_ioctl+0x4aa/0x1a60 block/ioctl.c:590
 [<ffffffff8162849e>] block_ioctl+0xde/0x120 fs/block_dev.c:1688
 [<ffffffff815aa5da>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815aa5da>] do_vfs_ioctl+0x1aa/0x1140 fs/ioctl.c:679
 [<ffffffff815ab5ff>] SYSC_ioctl fs/ioctl.c:694 [inline]
 [<ffffffff815ab5ff>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff838a9985>] entry_SYSCALL_64_fastpath+0x23/0xc6

Showing all locks held in the system:
3 locks held by kworker/u4:0/6:
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff811876e9>] __write_once_size include/linux/compiler.h:272 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff811876e9>] atomic64_set arch/x86/include/asm/atomic64_64.h:33 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff811876e9>] atomic_long_set include/asm-generic/atomic-long.h:56 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff811876e9>] set_work_data kernel/workqueue.c:616 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff811876e9>] set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff811876e9>] process_one_work+0x6a9/0x15f0 kernel/workqueue.c:2083
 #1:  (net_cleanup_work){+.+.+.}, at: [<ffffffff8118771b>] process_one_work+0x6db/0x15f0 kernel/workqueue.c:2087
 #2:  (net_mutex){+.+.+.}, at: [<ffffffff82f144df>] cleanup_net+0x13f/0x610 net/core/net_namespace.c:420
2 locks held by khungtaskd/514:
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136fe05>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136fe05>] watchdog+0x125/0xa70 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff812355d0>] debug_show_all_locks+0x70/0x280 kernel/locking/lockdep.c:4336
1 lock held by rsyslogd/3153:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<ffffffff815cf91f>] __fdget_pos+0x9f/0xc0 fs/file.c:781
2 locks held by getty/3243:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838a7b92>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff82001d84>] n_tty_read+0x1f4/0x16c0 drivers/tty/n_tty.c:2133
1 lock held by syz-executor2/3786:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff824ae90f>] lo_ioctl+0x8f/0x1990 drivers/block/loop.c:1337
1 lock held by syz-executor2/3804:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff824ae90f>] lo_ioctl+0x8f/0x1990 drivers/block/loop.c:1337

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

NMI backtrace for cpu 1
CPU: 1 PID: 514 Comm: khungtaskd Not tainted 4.9.66-g87cdf4e #104
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d8e37d00 ffffffff81d90749 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810ba170 ffff8801d8e37d38
 ffffffff81d9b86d 0000000000000001 0000000000000000 ffff8801cf006418
Call Trace:
 [<ffffffff81d90749>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d90749>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81d9b86d>] nmi_cpu_backtrace+0xfd/0x120 lib/nmi_backtrace.c:99
 [<ffffffff81d9b9a7>] nmi_trigger_cpumask_backtrace+0x117/0x190 lib/nmi_backtrace.c:60
 [<ffffffff810ba264>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff813703d0>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff813703d0>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff813703d0>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff813703d0>] watchdog+0x6f0/0xa70 kernel/hung_task.c:239
 [<ffffffff811985ad>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838a9c2a>] ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:437
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at pc 0xffffffff838a8606