INFO: task syz-executor542:3910 blocked for more than 120 seconds.
      Not tainted 4.9.108-gb7d377b #50
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor542 D28232  3910   3907 0x00000000
 ffff8801d68fc800 0000000000000000 ffff8801d72f2f40 ffffffff84629800
 ffff8801db221c18 ffff8801d55079c8 ffffffff839e8aed ffff8801d68fd0c8
 ffffed003ad1fa18 ffff8801d68fc800 00fffc0000000000 ffff8801db2224e8
Call Trace:
 [<ffffffff839ea0ef>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839eaa73>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3590
 [<ffffffff839eeef6>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff839eeef6>] mutex_lock_nested+0x326/0x870 kernel/locking/mutex.c:621
 [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
 [<ffffffff81e57a26>] __blkdev_driver_ioctl block/ioctl.c:294 [inline]
 [<ffffffff81e57a26>] blkdev_ioctl+0x7b6/0x1a70 block/ioctl.c:590
 [<ffffffff81632b8e>] block_ioctl+0xde/0x120 fs/block_dev.c:1688
 [<ffffffff815b2b9c>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815b2b9c>] file_ioctl fs/ioctl.c:493 [inline]
 [<ffffffff815b2b9c>] do_vfs_ioctl+0x1ac/0x11a0 fs/ioctl.c:677
 [<ffffffff815b3c1f>] SYSC_ioctl fs/ioctl.c:694 [inline]
 [<ffffffff815b3c1f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f99d3>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb

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/3773:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f7b92>] 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
1 lock held by syz-executor542/3910:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor542/3912:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor542/3914:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor542/3915:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor542/3916:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor542/3917:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor542/3918:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor542/3919:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor542/3920:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor542/3921:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor542/3923:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor542/3924:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor542/3925:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor542/3926:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor542/3927:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor542/3928:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by blkid/3931:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344

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

NMI backtrace for cpu 1
CPU: 1 PID: 519 Comm: khungtaskd Not tainted 4.9.108-gb7d377b #50
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d8617d08 ffffffff81eb3e29 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810b96a0 ffff8801d8617d40
 ffffffff81ebf127 0000000000000001 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
 [<ffffffff810b97a4>] 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
 [<ffffffff839f9b9c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 3907 Comm: sshd Not tainted 4.9.108-gb7d377b #50
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d5629800 task.stack: ffff8801d7808000
RIP: 0010:[<ffffffff811bb1e1>] 
c [<ffffffff811bb1e1>] preempt_count_sub+0x11/0x160 kernel/sched/core.c:3269
RSP: 0018:ffff8801d780f318  EFLAGS: 00000202
RAX: dffffc0000000000 RBX: 0000000000000001 RCX: 1ffffffff0886480
RDX: 1ffffffff08dc2b3 RSI: ffffffff81f1b88b RDI: 0000000000000001
RBP: ffff8801d780f320 R08: ffff8801d562a0e8 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff846e1540
R13: 0000000000000001 R14: ffff8801d780f4b0 R15: ffff8801cf8f3c00
FS:  00007f2182b417c0(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f21829b0f70 CR3: 00000001c5058000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 0000000000000001
c ffff8801d780f350
c ffffffff81284152
c ffff8801d780f350
c
 dffffc0000000000
c ffff8801d780f3f8
c ffff8801cdc78900
c ffff8801d780f360
c
 ffffffff8127c100
c ffff8801d780f3b8
c ffffffff831da487
c ffffffff84b59200
c
Call Trace:
 [<ffffffff81284152>] rcu_lockdep_current_cpu_online+0xf2/0x140 kernel/rcu/tree.c:1109
 [<ffffffff8127c100>] rcu_read_lock_held+0x90/0xc0 kernel/rcu/update.c:295
 [<ffffffff831da487>] nf_iterate+0x217/0x310 net/netfilter/core.c:339
 [<ffffffff831da694>] nf_hook_slow+0x114/0x1e0 net/netfilter/core.c:355
 [<ffffffff8333bcac>] nf_hook_thresh include/linux/netfilter.h:191 [inline]
 [<ffffffff8333bcac>] nf_hook include/linux/netfilter.h:203 [inline]
 [<ffffffff8333bcac>] __ip_local_out+0x42c/0x5b0 net/ipv4/ip_output.c:113
 [<ffffffff8333be59>] ip_local_out+0x29/0x180 net/ipv4/ip_output.c:122
 [<ffffffff8333d2c7>] ip_queue_xmit+0x897/0x1ba0 net/ipv4/ip_output.c:500
 [<ffffffff833a524c>] tcp_transmit_skb+0x168c/0x2e30 net/ipv4/tcp_output.c:1036
 [<ffffffff833a7abb>] tcp_write_xmit+0x10cb/0x4c40 net/ipv4/tcp_output.c:2209
 [<ffffffff833ab6d0>] __tcp_push_pending_frames+0xa0/0x240 net/ipv4/tcp_output.c:2390
 [<ffffffff8335b45e>] tcp_push+0x3fe/0x5e0 net/ipv4/tcp.c:688
 [<ffffffff8336cd40>] tcp_sendmsg+0x1110/0x3040 net/ipv4/tcp.c:1348
 [<ffffffff83429c53>] inet_sendmsg+0x203/0x4d0 net/ipv4/af_inet.c:770
 [<ffffffff83016fcc>] sock_sendmsg_nosec net/socket.c:635 [inline]
 [<ffffffff83016fcc>] sock_sendmsg+0xcc/0x110 net/socket.c:645
 [<ffffffff83017233>] sock_write_iter+0x223/0x3b0 net/socket.c:843
 [<ffffffff8156eb60>] new_sync_write fs/read_write.c:496 [inline]
 [<ffffffff8156eb60>] __vfs_write+0x3e0/0x580 fs/read_write.c:509
 [<ffffffff81572957>] vfs_write+0x187/0x530 fs/read_write.c:557
 [<ffffffff81576789>] SYSC_write fs/read_write.c:604 [inline]
 [<ffffffff81576789>] SyS_write+0xd9/0x1c0 fs/read_write.c:596
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f99d3>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 
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c<48> 
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c