INFO: task syz-executor0:3846 blocked for more than 140 seconds.
      Not tainted 4.4.139-g7ba5557 #2
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor0   D ffff8801c15a79c8 27408  3846      1 0x20020004
 ffff8801c15a79c8 0000000000000000 ffff8801c91a68e0 ffffed0039234d1b
 ffff8801c91a6000 ffff8801db31fdb8 ffff8801db31fde0 ffff8801db31f4d8
 ffff8801db31f4c0 ffff8801d9a41800 ffff8801c91a6000 0000000000000000
Call Trace:
 [<ffffffff838b381a>] schedule+0x7a/0x1b0 kernel/sched/core.c:3359
 [<ffffffff838b3fb3>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3392
 [<ffffffff838ba0f7>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff838ba0f7>] mutex_lock_nested+0x307/0x850 kernel/locking/mutex.c:621
 [<ffffffff8251a51b>] lo_ioctl+0x8b/0x1ad0 drivers/block/loop.c:1355
 [<ffffffff8251c012>] lo_compat_ioctl+0xb2/0x140 drivers/block/loop.c:1551
 [<ffffffff81dff095>] compat_blkdev_ioctl+0x395/0x3a10 block/compat_ioctl.c:751
 [<ffffffff81628a04>] C_SYSC_ioctl fs/compat_ioctl.c:1592 [inline]
 [<ffffffff81628a04>] compat_SyS_ioctl+0x484/0x2270 fs/compat_ioctl.c:1544
 [<ffffffff81006d96>] do_syscall_32_irqs_on arch/x86/entry/common.c:392 [inline]
 [<ffffffff81006d96>] do_fast_syscall_32+0x326/0x8b0 arch/x86/entry/common.c:459
 [<ffffffff838c31aa>] sysenter_flags_fixed+0xd/0x17
1 lock held by syz-executor0/3846:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff8251a51b>] lo_ioctl+0x8b/0x1ad0 drivers/block/loop.c:1355
Sending NMI to all CPUs:
NMI backtrace for cpu 0
CPU: 0 PID: 13838 Comm: syz-executor4 Not tainted 4.4.139-g7ba5557 #2
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d9b8c800 task.stack: ffff8801ca620000
RIP: 0010:[<ffffffff813514fb>]  [<ffffffff813514fb>] __write_once_size include/linux/compiler.h:247 [inline]
RIP: 0010:[<ffffffff813514fb>]  [<ffffffff813514fb>] __sanitizer_cov_trace_pc+0x4b/0x50 kernel/kcov.c:108
RSP: 0018:ffff8801ca627ae8  EFLAGS: 00000246
RAX: 0000000000040000 RBX: ffff8800b9cc8760 RCX: ffffc90006645000
RDX: 0000000000040000 RSI: ffffffff8251ba3a RDI: ffff8801d6580db0
RBP: ffff8801ca627ae8 R08: ffff8801d9b8d128 R09: 0000000000000001
R10: 0000000000000000 R11: ffff8801d9b8c800 R12: ffff8800b9cc8760
R13: ffff8801d33a33c0 R14: ffff8801d7316880 R15: ffff8801d73169d8
FS:  0000000000000000(0000) GS:ffff8801db200000(0063) knlGS:00000000f574cb40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 00007f75dd9bf000 CR3: 00000000ad5fb000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff8801ca627b78 ffffffff8251ba3a ffff8801ca627af0 ffff880100000000
 ffff8801d69a4498 ffff8801d73169d0 ffff8800af426000 ffff8801d69a4498
 ffff8800b9cc8948 ffff8800af423200 ffff8801d33a34b0 dffffc000002001d
Call Trace:
 [<ffffffff8251ba3a>] is_loop_device drivers/block/loop.c:715 [inline]
 [<ffffffff8251ba3a>] loop_set_fd drivers/block/loop.c:897 [inline]
 [<ffffffff8251ba3a>] lo_ioctl+0x15aa/0x1ad0 drivers/block/loop.c:1358
 [<ffffffff8251c012>] lo_compat_ioctl+0xb2/0x140 drivers/block/loop.c:1551
 [<ffffffff81dff095>] compat_blkdev_ioctl+0x395/0x3a10 block/compat_ioctl.c:751
 [<ffffffff81628a04>] C_SYSC_ioctl fs/compat_ioctl.c:1592 [inline]
 [<ffffffff81628a04>] compat_SyS_ioctl+0x484/0x2270 fs/compat_ioctl.c:1544
 [<ffffffff81006d96>] do_syscall_32_irqs_on arch/x86/entry/common.c:392 [inline]
 [<ffffffff81006d96>] do_fast_syscall_32+0x326/0x8b0 arch/x86/entry/common.c:459
 [<ffffffff838c31aa>] sysenter_flags_fixed+0xd/0x17
Code: 8b 90 98 12 00 00 83 fa 02 75 20 48 8b 88 a0 12 00 00 8b 80 9c 12 00 00 48 8b 11 48 83 c2 01 48 39 d0 76 07 48 89 34 d1 48 89 11 <5d> c3 0f 1f 00 55 48 89 e5 41 57 41 56 41 55 41 54 53 48 89 f3 
NMI backtrace for cpu 1
CPU: 1 PID: 491 Comm: khungtaskd Not tainted 4.4.139-g7ba5557 #2
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8800bb3fc800 task.stack: ffff8801d92d0000
RIP: 0010:[<ffffffff810bfb46>]  [<ffffffff810bfb46>] native_apic_mem_write arch/x86/include/asm/apic.h:94 [inline]
RIP: 0010:[<ffffffff810bfb46>]  [<ffffffff810bfb46>] __default_send_IPI_dest_field arch/x86/include/asm/ipi.h:119 [inline]
RIP: 0010:[<ffffffff810bfb46>]  [<ffffffff810bfb46>] _flat_send_IPI_mask arch/x86/kernel/apic/apic_flat_64.c:61 [inline]
RIP: 0010:[<ffffffff810bfb46>]  [<ffffffff810bfb46>] flat_send_IPI_mask+0xf6/0x1a0 arch/x86/kernel/apic/apic_flat_64.c:69
RSP: 0018:ffff8801d92d7cc8  EFLAGS: 00000046
RAX: 0000000003000000 RBX: 0000000000000c00 RCX: 0000000000000000
RDX: 0000000000000c00 RSI: 0000000000000000 RDI: ffffffffff5fb300
RBP: ffff8801d92d7cf0 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000001 R12: 0000000000000246
R13: 0000000000000003 R14: 0000000000000002 R15: ffffffff8446f6a0
FS:  0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fb1f4c32000 CR3: 00000001d2fe6000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff8446f6a0 ffffffff84a18ca0 0000000000000007 fffffbfff0942c44
 0000000000000040 ffff8801d92d7d10 ffffffff810b5b01 ffffffff83c0b2a0
 0000000000000003 ffff8801d92d7d68 ffffffff81e18603 ffffffff8140dd6f
Call Trace:
 [<ffffffff810b5b01>] nmi_raise_cpu_backtrace+0x61/0x80 arch/x86/kernel/apic/hw_nmi.c:33
 [<ffffffff81e18603>] nmi_trigger_all_cpu_backtrace.cold.4+0x70/0xad lib/nmi_backtrace.c:85
 [<ffffffff810b5ba4>] 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
 [<ffffffff838c1c95>] 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 e2