INFO: task syz-executor048:3811 blocked for more than 120 seconds.
      Not tainted 4.9.109-g7143cbf #3
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor048 D28088  3811   3808 0x00000000
 ffff8801d7440000 0000000000000000 ffff8801d7870000 ffff8801d9a6b000
 ffff8801db321c18 ffff8801c6d9f9c8 ffffffff839e8a3d ffff8801d74408c8
 ffffed003ae88118 ffff8801d7440000 00fffc0000000000 ffff8801db3224e8
Call Trace:
 [<ffffffff839ea03f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839ea9c3>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3590
 [<ffffffff839eee46>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff839eee46>] 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
 [<ffffffff839f9913>] 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/3694:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f7ae2>] 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-executor048/3811:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor048/3813:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor048/3814:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor048/3816:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor048/3817:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor048/3818:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor048/3819:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor048/3820:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor048/3821:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor048/3822:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor048/3823:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor048/3824:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor048/3825:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor048/3826:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor048/3827:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor048/3828:
 #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 4.9.109-g7143cbf #3
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d8a47d08 ffffffff81eb3e29 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810b9580 ffff8801d8a47d40
 ffffffff81ebf127 0000000000000001 0000000000000000 0000000000000002
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
 [<ffffffff810b9684>] 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
 [<ffffffff839f9adc>] 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: 3808 Comm: sshd Not tainted 4.9.109-g7143cbf #3
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d76f9800 task.stack: ffff8801d72c0000
RIP: 0010:[<ffffffff81f1b9dc>] 
c [<ffffffff81f1b9dc>] debug_smp_processor_id+0x1c/0x20 lib/smp_processor_id.c:56
RSP: 0018:ffff8801d72c6ef8  EFLAGS: 00000296
RAX: 0000000000000000 RBX: ffffffff84870b20 RCX: 0000000000000002
RDX: 0000000000000000 RSI: ffffffff81f1b88b RDI: ffffffff83e2d9e0
RBP: ffff8801d72c6ef8 R08: ffffed003ae58d8e R09: 00000000f4383906
R10: ffffffff83038df0 R11: ffff8801d72c6c6f R12: 00000000000000e0
R13: ffff8801c99733c0 R14: 0000000002080020 R15: 0000000000000140
FS:  00007f68988187c0(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000556d676d4ff0 CR3: 00000001c872f000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff8801d72c6f18
c ffffffff8127f515
c ffff8801c99733c0
c ffffffff84870b20
c
 ffff8801d72c6f30
c ffffffff8127bfdd
c ffff8801c99738c0
c ffff8801d72c6f70
c
 ffffffff81536eb3
c ffffffff8307a640
c ffff8801bf474fe0
c ffff8801d8a7bd40
c
Call Trace:
 [<ffffffff8127f515>] __rcu_is_watching kernel/rcu/tree.c:1053 [inline]
 [<ffffffff8127f515>] rcu_is_watching+0x15/0xa0 kernel/rcu/tree.c:1067
 [<ffffffff8127bfdd>] rcu_read_lock_sched_held+0x8d/0x120 kernel/rcu/update.c:107
 [<ffffffff81536eb3>] trace_kmem_cache_alloc include/trace/events/kmem.h:53 [inline]
 [<ffffffff81536eb3>] kmem_cache_alloc+0x223/0x290 mm/slub.c:2730
 [<ffffffff83038df0>] skb_clone+0x140/0x2c0 net/core/skbuff.c:1033
 [<ffffffff8307a8e7>] dev_queue_xmit_nit+0x2a7/0x820 net/core/dev.c:1897
 [<ffffffff83089896>] xmit_one net/core/dev.c:2951 [inline]
 [<ffffffff83089896>] dev_hard_start_xmit+0xa6/0x8b0 net/core/dev.c:2971
 [<ffffffff8312267c>] sch_direct_xmit+0x2bc/0x590 net/sched/sch_generic.c:182
 [<ffffffff8308baa2>] __dev_xmit_skb net/core/dev.c:3151 [inline]
 [<ffffffff8308baa2>] __dev_queue_xmit+0x1742/0x2080 net/core/dev.c:3419
 [<ffffffff8308c3f7>] dev_queue_xmit+0x17/0x20 net/core/dev.c:3484
 [<ffffffff833385bb>] neigh_hh_output include/net/neighbour.h:468 [inline]
 [<ffffffff833385bb>] dst_neigh_output include/net/dst.h:468 [inline]
 [<ffffffff833385bb>] ip_finish_output2+0xcab/0x1110 net/ipv4/ip_output.c:225
 [<ffffffff8333b1e8>] ip_finish_output+0x468/0xb00 net/ipv4/ip_output.c:313
 [<ffffffff8333f4ed>] NF_HOOK_COND include/linux/netfilter.h:246 [inline]
 [<ffffffff8333f4ed>] ip_output+0x1cd/0x550 net/ipv4/ip_output.c:401
 [<ffffffff8333becb>] dst_output include/net/dst.h:507 [inline]
 [<ffffffff8333becb>] ip_local_out+0x9b/0x180 net/ipv4/ip_output.c:124
 [<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
 [<ffffffff839f9913>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 
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c<5d> 
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c