INFO: task syz-executor0:17023 blocked for more than 120 seconds.
      Not tainted 4.4.131-g4fca5a0 #32
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor0   D ffff8801a07179e0 29344 17023   3920 0x20020004
 ffff8801a07179e0 0000000000000246 0000000000000292 0000000041b58ab3
 ffffffff841e1300 ffff8801db21fdb8 ffff8801db21fde0 ffff8801db21f4d8
 ffff8801db21f4c0 ffffffff84417840 ffff88008a2c0000 0000000000000000
Call Trace:
 [<ffffffff838b1dea>] schedule+0x7a/0x1b0 kernel/sched/core.c:3359
 [<ffffffff81da0b80>] blk_mq_freeze_queue_wait+0x120/0x240 block/blk-mq.c:95
 [<ffffffff81da927d>] blk_freeze_queue block/blk-mq.c:112 [inline]
 [<ffffffff81da927d>] blk_mq_freeze_queue+0x1d/0x20 block/blk-mq.c:121
 [<ffffffff8251b3c2>] loop_switch drivers/block/loop.c:610 [inline]
 [<ffffffff8251b3c2>] loop_change_fd drivers/block/loop.c:696 [inline]
 [<ffffffff8251b3c2>] lo_ioctl+0x722/0x1ad0 drivers/block/loop.c:1361
 [<ffffffff8251c822>] lo_compat_ioctl+0xb2/0x140 drivers/block/loop.c:1551
 [<ffffffff81dffb75>] compat_blkdev_ioctl+0x395/0x3a10 block/compat_ioctl.c:751
 [<ffffffff81628144>] C_SYSC_ioctl fs/compat_ioctl.c:1592 [inline]
 [<ffffffff81628144>] 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
 [<ffffffff838c176a>] sysenter_flags_fixed+0xd/0x17
1 lock held by syz-executor0/17023:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff8251ad2b>] lo_ioctl+0x8b/0x1ad0 drivers/block/loop.c:1355
Sending NMI to all CPUs:
NMI backtrace for cpu 0
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.4.131-g4fca5a0 #32
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffffffff84417840 task.stack: ffffffff84400000
RIP: 0010:[<ffffffff8122e482>]  [<ffffffff8122e482>] trace_hardirqs_on_caller+0x172/0x590 kernel/locking/lockdep.c:2601
RSP: 0018:ffffffff84407ca8  EFLAGS: 00000802
RAX: dffffc0000000000 RBX: 0000000000000003 RCX: 1ffffffff0942908
RDX: 1ffffffff0942379 RSI: ffffffff81e6dbfb RDI: ffffffff84a11bc8
RBP: ffffffff84407cb8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff838c0a29
R13: 0000000000000000 R14: fffffbfff074890c R15: ffffffff84a05aa8
FS:  0000000000000000(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000a48000 CR3: 00000000b66d4000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff84a05aa8 0000000000000000 ffffffff84407dc8 ffffffff81003017
 0000000000000000 0000000000000000 0000000000000000 0000000000000000
 0000000000000001 1ffffffff0942908 1ffff1003b643ea8 ffffffff81e6dbfb
Call Trace:
 [<ffffffff81003017>] trace_hardirqs_on_thunk+0x17/0x19
 [<ffffffff81025da5>] arch_safe_halt arch/x86/include/asm/paravirt.h:117 [inline]
 [<ffffffff81025da5>] default_idle+0x55/0x3c0 arch/x86/kernel/process.c:290
 [<ffffffff810272f0>] arch_cpu_idle+0x10/0x20 arch/x86/kernel/process.c:281
 [<ffffffff8121b9e7>] default_idle_call+0x57/0x70 kernel/sched/idle.c:93
 [<ffffffff8121c18f>] cpuidle_idle_call kernel/sched/idle.c:157 [inline]
 [<ffffffff8121c18f>] cpu_idle_loop kernel/sched/idle.c:253 [inline]
 [<ffffffff8121c18f>] cpu_startup_entry+0x6af/0x780 kernel/sched/idle.c:301
 [<ffffffff838acf51>] rest_init+0x188/0x18e init/main.c:410
 [<ffffffff84a4b8a1>] start_kernel+0x6b3/0x6e7 init/main.c:682
 [<ffffffff84a4a30f>] x86_64_start_reservations+0x29/0x2b arch/x86/kernel/head64.c:196
 [<ffffffff84a4a450>] x86_64_start_kernel+0x13f/0x162 arch/x86/kernel/head64.c:185
Code: 85 0e 03 00 00 8b 3d de 01 70 04 85 ff 0f 85 83 00 00 00 48 c7 c7 c8 1b a1 84 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <0f> b6 04 02 48 89 fa 83 e2 07 38 d0 7f 08 84 c0 0f 85 c8 02 00 
NMI backtrace for cpu 1
CPU: 1 PID: 491 Comm: khungtaskd Not tainted 4.4.131-g4fca5a0 #32
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8800badd4800 task.stack: ffff8801d8f18000
RIP: 0010:[<ffffffff810bfda6>]  [<ffffffff810bfda6>] native_apic_mem_write arch/x86/include/asm/apic.h:94 [inline]
RIP: 0010:[<ffffffff810bfda6>]  [<ffffffff810bfda6>] __default_send_IPI_dest_field arch/x86/include/asm/ipi.h:119 [inline]
RIP: 0010:[<ffffffff810bfda6>]  [<ffffffff810bfda6>] _flat_send_IPI_mask arch/x86/kernel/apic/apic_flat_64.c:61 [inline]
RIP: 0010:[<ffffffff810bfda6>]  [<ffffffff810bfda6>] flat_send_IPI_mask+0xf6/0x1a0 arch/x86/kernel/apic/apic_flat_64.c:69
RSP: 0018:ffff8801d8f1fcc8  EFLAGS: 00000046
RAX: 0000000003000000 RBX: 0000000000000c00 RCX: 0000000000000000
RDX: 0000000000000c00 RSI: 0000000000000000 RDI: ffffffffff5fb300
RBP: ffff8801d8f1fcf0 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: 00007f16c3f07000 CR3: 00000001cc519000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff8446f7a0 ffffffff84a189e0 0000000000000007 fffffbfff0942bec
 0000000000000040 ffff8801d8f1fd10 ffffffff810b5d61 ffffffff83c0b1a0
 0000000000000003 ffff8801d8f1fd68 ffffffff81e190e3 ffffffff8140daaf
Call Trace:
 [<ffffffff810b5d61>] nmi_raise_cpu_backtrace+0x61/0x80 arch/x86/kernel/apic/hw_nmi.c:33
 [<ffffffff81e190e3>] nmi_trigger_all_cpu_backtrace.cold.4+0x70/0xad lib/nmi_backtrace.c:85
 [<ffffffff810b5e04>] arch_trigger_all_cpu_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
 [<ffffffff8141a199>] trigger_all_cpu_backtrace include/linux/nmi.h:44 [inline]
 [<ffffffff8141a199>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff8141a199>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff8141a199>] watchdog.cold.1+0xd3/0xee kernel/hung_task.c:238
 [<ffffffff81190768>] kthread+0x268/0x300 kernel/kthread.c:211
 [<ffffffff838c0255>] 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 62