INFO: task syz-executor0:3881 blocked for more than 140 seconds.
      Not tainted 4.4.140-ged9bdc8 #4
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor0   D ffff8801c0e2f9c8 26720  3881      1 0x20020004
 ffff8801c0e2f9c8 0000000000000000 ffff8800ac0350e0 ffffed0015806a1b
 ffff8800ac034800 ffff8801db21fdb8 ffff8801db21fde0 ffff8801db21f4d8
 ffff8801db21f4c0 ffff8801c6071800 ffff8800ac034800 0000000000000000
Call Trace:
 [<ffffffff838b476a>] schedule+0x7a/0x1b0 kernel/sched/core.c:3359
 [<ffffffff838b4f03>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3392
 [<ffffffff838bb047>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff838bb047>] mutex_lock_nested+0x307/0x850 kernel/locking/mutex.c:621
 [<ffffffff8251b0ab>] lo_ioctl+0x8b/0x1ad0 drivers/block/loop.c:1355
 [<ffffffff8251cba2>] lo_compat_ioctl+0xb2/0x140 drivers/block/loop.c:1551
 [<ffffffff81dffb95>] compat_blkdev_ioctl+0x395/0x3a10 block/compat_ioctl.c:751
 [<ffffffff81628a44>] C_SYSC_ioctl fs/compat_ioctl.c:1592 [inline]
 [<ffffffff81628a44>] 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
 [<ffffffff838c40ea>] sysenter_flags_fixed+0xd/0x17
1 lock held by syz-executor0/3881:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff8251b0ab>] lo_ioctl+0x8b/0x1ad0 drivers/block/loop.c:1355
Sending NMI to all CPUs:
NMI backtrace for cpu 0
CPU: 0 PID: 15927 Comm: syz-executor5 Not tainted 4.4.140-ged9bdc8 #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8800abf80000 task.stack: ffff8800b6af8000
RIP: 0010:[<ffffffff8135153b>]  [<ffffffff8135153b>] __write_once_size include/linux/compiler.h:247 [inline]
RIP: 0010:[<ffffffff8135153b>]  [<ffffffff8135153b>] __sanitizer_cov_trace_pc+0x4b/0x50 kernel/kcov.c:108
RSP: 0018:ffff8800b6affae8  EFLAGS: 00000246
RAX: 0000000000040000 RBX: ffff8800b9cd0b80 RCX: ffffc900050a6000
RDX: 0000000000040000 RSI: ffffffff8251c642 RDI: ffff8800b9cd1070
RBP: ffff8800b6affae8 R08: ffff8800abf80928 R09: 0000000000000001
R10: 0000000000000000 R11: ffff8800abf80000 R12: ffff8800b9cd0d20
R13: ffff8800b9e50000 R14: ffff8800b90d8480 R15: ffff8800b90d85d8
FS:  0000000000000000(0000) GS:ffff8801db200000(0063) knlGS:00000000f572ab40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 000000000121fb10 CR3: 00000001c8af6000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff8800b6affb78 ffffffff8251c642 ffff8801c7c5a060 ffff880000000001
 ffffffff00000000 ffff8800b90d85d0 ffff8800b6af6000 ffff8800b6affb18
 ffff8800b9cd0f08 ffff8801d1b1c200 ffff8800b9e500f0 dffffc000002001d
Call Trace:
 [<ffffffff8251c642>] loop_set_fd drivers/block/loop.c:903 [inline]
 [<ffffffff8251c642>] lo_ioctl+0x1622/0x1ad0 drivers/block/loop.c:1358
 [<ffffffff8251cba2>] lo_compat_ioctl+0xb2/0x140 drivers/block/loop.c:1551
 [<ffffffff81dffb95>] compat_blkdev_ioctl+0x395/0x3a10 block/compat_ioctl.c:751
 [<ffffffff81628a44>] C_SYSC_ioctl fs/compat_ioctl.c:1592 [inline]
 [<ffffffff81628a44>] 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
 [<ffffffff838c40ea>] 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 4.4.140-ged9bdc8 #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8800bb0fb000 task.stack: ffff8801d92a8000
RIP: 0010:[<ffffffff810bff96>]  [<ffffffff810bff96>] native_apic_mem_write arch/x86/include/asm/apic.h:94 [inline]
RIP: 0010:[<ffffffff810bff96>]  [<ffffffff810bff96>] __default_send_IPI_dest_field arch/x86/include/asm/ipi.h:119 [inline]
RIP: 0010:[<ffffffff810bff96>]  [<ffffffff810bff96>] _flat_send_IPI_mask arch/x86/kernel/apic/apic_flat_64.c:61 [inline]
RIP: 0010:[<ffffffff810bff96>]  [<ffffffff810bff96>] flat_send_IPI_mask+0xf6/0x1a0 arch/x86/kernel/apic/apic_flat_64.c:69
RSP: 0018:ffff8801d92afcc8  EFLAGS: 00000046
RAX: 0000000003000000 RBX: 0000000000000c00 RCX: 0000000000000000
RDX: 0000000000000c00 RSI: 0000000000000000 RDI: ffffffffff5fb300
RBP: ffff8801d92afcf0 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000001 R12: 0000000000000246
R13: 0000000000000003 R14: 0000000000000002 R15: ffffffff8446f6e0
FS:  0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000001221000 CR3: 00000000b3df3000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff8446f6e0 ffffffff84a19060 0000000000000007 fffffbfff0942cbc
 0000000000000040 ffff8801d92afd10 ffffffff810b5f51 ffffffff83c0b760
 0000000000000003 ffff8801d92afd68 ffffffff81e19103 ffffffff8140ddaf
Call Trace:
 [<ffffffff810b5f51>] nmi_raise_cpu_backtrace+0x61/0x80 arch/x86/kernel/apic/hw_nmi.c:33
 [<ffffffff81e19103>] nmi_trigger_all_cpu_backtrace.cold.4+0x70/0xad lib/nmi_backtrace.c:85
 [<ffffffff810b5ff4>] arch_trigger_all_cpu_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
 [<ffffffff8141a499>] trigger_all_cpu_backtrace include/linux/nmi.h:44 [inline]
 [<ffffffff8141a499>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff8141a499>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff8141a499>] watchdog.cold.1+0xd3/0xee kernel/hung_task.c:238
 [<ffffffff81190998>] kthread+0x268/0x300 kernel/kthread.c:211
 [<ffffffff838c2bd5>] 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 d2