INFO: task syz-executor542:3898 blocked for more than 120 seconds.
      Not tainted 4.4.137-ga2e2217 #61
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor542 D ffff8800baebfa68 27504  3898   3895 0x00000000
 ffff8800baebfa68 0000000000000000 ffff8801d86e20e0 ffffed003b0dc41b
 ffff8801d86e1800 ffff8801db21fdb8 ffff8801db21fde0 ffff8801db21f4d8
 ffff8801db21f4c0 ffffffff84417840 ffff8801d86e1800 0000000000000000
Call Trace:
 [<ffffffff838b489a>] schedule+0x7a/0x1b0 kernel/sched/core.c:3359
 [<ffffffff838b5033>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3392
 [<ffffffff838bb177>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff838bb177>] mutex_lock_nested+0x307/0x850 kernel/locking/mutex.c:621
 [<ffffffff8251bd0b>] lo_ioctl+0x8b/0x1ad0 drivers/block/loop.c:1355
 [<ffffffff81db8068>] __blkdev_driver_ioctl block/ioctl.c:288 [inline]
 [<ffffffff81db8068>] blkdev_ioctl+0x7b8/0x19c0 block/ioctl.c:584
 [<ffffffff815d3fce>] block_ioctl+0xde/0x120 fs/block_dev.c:1625
 [<ffffffff81559c8f>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff81559c8f>] file_ioctl fs/ioctl.c:470 [inline]
 [<ffffffff81559c8f>] do_vfs_ioctl+0x63f/0xf40 fs/ioctl.c:605
 [<ffffffff8155a61f>] SYSC_ioctl fs/ioctl.c:622 [inline]
 [<ffffffff8155a61f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:613
 [<ffffffff838c28e5>] entry_SYSCALL_64_fastpath+0x22/0x9e
1 lock held by syz-executor542/3898:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff8251bd0b>] lo_ioctl+0x8b/0x1ad0 drivers/block/loop.c:1355
Sending NMI to all CPUs:
NMI backtrace for cpu 0
CPU: 0 PID: 3897 Comm: syz-executor542 Not tainted 4.4.137-ga2e2217 #61
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d89b0000 task.stack: ffff8800bb210000
RIP: 0033:[<0000000000400a44>]  [<0000000000400a44>] 0x400a44
RSP: 002b:00007ffd131a5410  EFLAGS: 00000202
RAX: 0000000000000001 RBX: 00000000006dad10 RCX: 0000000000449489
RDX: 0000000000000012 RSI: 00000000004adf5d RDI: 000000000000000c
RBP: 000000000000000a R08: 00000000004002e0 R09: 00000000004002e0
R10: 00000000004002e0 R11: 0000000000000206 R12: 00000000006dad14
R13: 00000000006dada0 R14: 0000000000000007 R15: 000000000000000c
FS:  0000000000dd4880(0063) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000001753000 CR3: 00000000ad27e000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

NMI backtrace for cpu 1
CPU: 1 PID: 492 Comm: khungtaskd Not tainted 4.4.137-ga2e2217 #61
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8800bb056000 task.stack: ffff8800bb0d0000
RIP: 0010:[<ffffffff810bfeb6>]  [<ffffffff810bfeb6>] native_apic_mem_write arch/x86/include/asm/apic.h:94 [inline]
RIP: 0010:[<ffffffff810bfeb6>]  [<ffffffff810bfeb6>] __default_send_IPI_dest_field arch/x86/include/asm/ipi.h:119 [inline]
RIP: 0010:[<ffffffff810bfeb6>]  [<ffffffff810bfeb6>] _flat_send_IPI_mask arch/x86/kernel/apic/apic_flat_64.c:61 [inline]
RIP: 0010:[<ffffffff810bfeb6>]  [<ffffffff810bfeb6>] flat_send_IPI_mask+0xf6/0x1a0 arch/x86/kernel/apic/apic_flat_64.c:69
RSP: 0018:ffff8800bb0d7cc8  EFLAGS: 00000046
RAX: 0000000003000000 RBX: 0000000000000c00 RCX: 0000000000000000
RDX: 0000000000000c00 RSI: 0000000000000000 RDI: ffffffffff5fb300
RBP: ffff8800bb0d7cf0 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000001 R12: 0000000000000246
R13: 0000000000000003 R14: 0000000000000002 R15: ffffffff8446f7a0
FS:  0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f25b7bd1000 CR3: 00000000bb10a000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff8446f7a0 ffffffff84a18ee0 0000000000000007 fffffbfff0942c8c
 0000000000000040 ffff8800bb0d7d10 ffffffff810b5e71 ffffffff83c0b560
 0000000000000003 ffff8800bb0d7d68 ffffffff81e19e83 ffffffff8140dd6f
Call Trace:
 [<ffffffff810b5e71>] nmi_raise_cpu_backtrace+0x61/0x80 arch/x86/kernel/apic/hw_nmi.c:33
 [<ffffffff81e19e83>] nmi_trigger_all_cpu_backtrace.cold.4+0x70/0xad lib/nmi_backtrace.c:85
 [<ffffffff810b5f14>] arch_trigger_all_cpu_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
 [<ffffffff8141a459>] trigger_all_cpu_backtrace include/linux/nmi.h:44 [inline]
 [<ffffffff8141a459>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff8141a459>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff8141a459>] watchdog.cold.1+0xd3/0xee kernel/hung_task.c:238
 [<ffffffff81190958>] kthread+0x268/0x300 kernel/kthread.c:211
 [<ffffffff838c2d15>] ret_from_fork+0x55/0x80 arch/x86/entry/entry_64.S:510
Code: b3 5f ff f6 c4 10 75 e2 44 89 e8 c1 e0 18 89 04 25 10 b3 5f ff 44 89 f2 09 da 80 cf 04 41 83 fe 02 0f 44 d3 89 14 25 00 b3 5f ff <41> f7 c4 00 02 00 00 75 1a 4c 89 e7 57 9d 0f 1f 44 00 00 e8 72