INFO: task syz-executor0:3877 blocked for more than 140 seconds.
      Not tainted 4.4.147-ga5fc665 #16
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor0   D ffff8800aa5afb08 25680  3877      1 0x20020004
 ffff8800aa5afb08 0000000000000001 ffff8801d93188e0 ffffed003b26311b
 ffff8801d9318000 ffff8801db31fe38 ffff8801db31fe60 ffff8801db31f558
 ffff8801db31f540 ffff8800a45bb000 ffff8801d9318000 0000000000000000
Call Trace:
 [<ffffffff838bac1a>] schedule+0x7a/0x1b0 kernel/sched/core.c:3355
 [<ffffffff838bb3b3>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3388
 [<ffffffff838c14f7>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff838c14f7>] mutex_lock_nested+0x307/0x850 kernel/locking/mutex.c:621
 [<ffffffff8252195f>] lo_release+0x1f/0x1a0 drivers/block/loop.c:1617
 [<ffffffff815d4926>] __blkdev_put+0x636/0x840 fs/block_dev.c:1535
 [<ffffffff815d59a5>] blkdev_put+0x85/0x560 fs/block_dev.c:1600
 [<ffffffff815d5f0b>] blkdev_close+0x8b/0xb0 fs/block_dev.c:1607
 [<ffffffff815253c5>] __fput+0x235/0x6f0 fs/file_table.c:208
 [<ffffffff81525905>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118e00f>] task_work_run+0x10f/0x190 kernel/task_work.c:115
 [<ffffffff8100362d>] tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 [<ffffffff8100362d>] exit_to_usermode_loop+0x13d/0x160 arch/x86/entry/common.c:253
 [<ffffffff8100708e>] prepare_exit_to_usermode arch/x86/entry/common.c:284 [inline]
 [<ffffffff8100708e>] syscall_return_slowpath arch/x86/entry/common.c:349 [inline]
 [<ffffffff8100708e>] do_syscall_32_irqs_on arch/x86/entry/common.c:399 [inline]
 [<ffffffff8100708e>] do_fast_syscall_32+0x61e/0x8b0 arch/x86/entry/common.c:460
 [<ffffffff838ca5c3>] sysenter_flags_fixed+0xd/0x1a
2 locks held by syz-executor0/3877:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff815d43ab>] __blkdev_put+0xbb/0x840 fs/block_dev.c:1516
 #1:  (loop_index_mutex){+.+.+.}, at: [<ffffffff8252195f>] lo_release+0x1f/0x1a0 drivers/block/loop.c:1617
Sending NMI to all CPUs:
NMI backtrace for cpu 0
CPU: 0 PID: 491 Comm: khungtaskd Not tainted 4.4.147-ga5fc665 #16
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8800bac98000 task.stack: ffff8800bac50000
RIP: 0010:[<ffffffff810c1c56>]  [<ffffffff810c1c56>] native_apic_mem_write arch/x86/include/asm/apic.h:93 [inline]
RIP: 0010:[<ffffffff810c1c56>]  [<ffffffff810c1c56>] __default_send_IPI_dest_field arch/x86/include/asm/ipi.h:119 [inline]
RIP: 0010:[<ffffffff810c1c56>]  [<ffffffff810c1c56>] _flat_send_IPI_mask arch/x86/kernel/apic/apic_flat_64.c:61 [inline]
RIP: 0010:[<ffffffff810c1c56>]  [<ffffffff810c1c56>] flat_send_IPI_mask+0xf6/0x1a0 arch/x86/kernel/apic/apic_flat_64.c:69
RSP: 0018:ffff8800bac57cc8  EFLAGS: 00000046
RAX: 0000000003000000 RBX: 0000000000000c00 RCX: 0000000000000000
RDX: 0000000000000c00 RSI: 0000000000000000 RDI: ffffffffff5fb300
RBP: ffff8800bac57cf0 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000001 R12: 0000000000000246
R13: 0000000000000003 R14: 0000000000000002 R15: ffffffff84470220
FS:  0000000000000000(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000d94258 CR3: 00000000afbf6000 CR4: 00000000001606f0
Stack:
 ffffffff84470220 ffffffff84a1a780 0000000000000007 fffffbfff0942fa4
 0000000000000040 ffff8800bac57d10 ffffffff810b7c11 ffffffff83c0d1a0
 0000000000000003 ffff8800bac57d68 ffffffff81e1dac3 ffffffff8141028f
Call Trace:
 [<ffffffff810b7c11>] nmi_raise_cpu_backtrace+0x61/0x80 arch/x86/kernel/apic/hw_nmi.c:33
 [<ffffffff81e1dac3>] nmi_trigger_all_cpu_backtrace.cold.4+0x70/0xad lib/nmi_backtrace.c:85
 [<ffffffff810b7cb4>] arch_trigger_all_cpu_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
 [<ffffffff8141c977>] trigger_all_cpu_backtrace include/linux/nmi.h:44 [inline]
 [<ffffffff8141c977>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff8141c977>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff8141c977>] watchdog.cold.1+0xd3/0xee kernel/hung_task.c:238
 [<ffffffff81192be8>] kthread+0x268/0x300 kernel/kthread.c:211
 [<ffffffff838c9095>] 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 
NMI backtrace for cpu 1
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.4.147-ga5fc665 #16
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d9a41800 task.stack: ffff8801d9a50000
RIP: 0010:[<ffffffff810ce336>]  [<ffffffff810ce336>] native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:49
RSP: 0018:ffff8801d9a57da0  EFLAGS: 00000246
RAX: 0000000000000007 RBX: ffffffff84a07868 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff8801d9a420dc
RBP: ffff8801d9a57da0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000001 R14: fffffbfff0748adc R15: ffffffff84a07868
FS:  0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000db17a8 CR3: 00000000afbf6000 CR4: 00000000001606f0
Stack:
 ffff8801d9a57dd8 ffffffff81025cd5 ffff8801d9a58000 0000000000000000
 0000000000000000 fffffbfff0748adc ffffffff84a07868 ffff8801d9a57de8
 ffffffff81027be0 ffff8801d9a57e00 ffffffff8121de97 dffffc0000000000
Call Trace:
 [<ffffffff81025cd5>] arch_safe_halt arch/x86/include/asm/paravirt.h:117 [inline]
 [<ffffffff81025cd5>] default_idle+0x55/0x3c0 arch/x86/kernel/process.c:432
 [<ffffffff81027be0>] arch_cpu_idle+0x10/0x20 arch/x86/kernel/process.c:423
 [<ffffffff8121de97>] default_idle_call+0x57/0x70 kernel/sched/idle.c:93
 [<ffffffff8121e63f>] cpuidle_idle_call kernel/sched/idle.c:157 [inline]
 [<ffffffff8121e63f>] cpu_idle_loop kernel/sched/idle.c:253 [inline]
 [<ffffffff8121e63f>] cpu_startup_entry+0x6af/0x780 kernel/sched/idle.c:301
 [<ffffffff810abf89>] start_secondary+0x329/0x400 arch/x86/kernel/smpboot.c:245
Code: 00 00 00 00 00 55 48 89 e5 fa 5d c3 66 0f 1f 84 00 00 00 00 00 55 48 89 e5 fb 5d c3 66 0f 1f 84 00 00 00 00 00 55 48 89 e5 fb f4 <5d> c3 0f 1f 84 00 00 00 00 00 55 48 89 e5 f4 5d c3 66 0f 1f 84