INFO: task syz-executor.0:2114 blocked for more than 140 seconds.
      Not tainted 4.4.174+ #4
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.0  D ffff8801c48a7648 25408  2114      1 0x00000004
 ffff8801c48a7648 ffff8801d5fd2f80 4f63ba5d46bcf0a6 ffff8801d5fd2f80
 0000000000000001 ffff8801d5fd3800 ffff8801db71f180 ffff8801db71f1a8
 ffff8801db71e898 ffff8801d5900000 ffff8801d5fd2f80 ffffed0038914001
Call Trace:
 [<ffffffff82709b79>] schedule+0x99/0x1d0 kernel/sched/core.c:3355
 [<ffffffff8270a333>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3388
 [<ffffffff8270c492>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff8270c492>] mutex_lock_nested+0x3c2/0xb80 kernel/locking/mutex.c:621
 [<ffffffff81d3d70d>] lo_open+0x1d/0xb0 drivers/block/loop.c:1633
 [<ffffffff8154f171>] __blkdev_get+0x8b1/0xdf0 fs/block_dev.c:1278
 [<ffffffff81551938>] blkdev_get+0x2e8/0x920 fs/block_dev.c:1353
 [<ffffffff8155219a>] blkdev_open+0x1aa/0x250 fs/block_dev.c:1508
 [<ffffffff8149154f>] do_dentry_open+0x38f/0xbd0 fs/open.c:749
 [<ffffffff81494d3b>] vfs_open+0x10b/0x210 fs/open.c:862
 [<ffffffff814c5ddf>] do_last fs/namei.c:3269 [inline]
 [<ffffffff814c5ddf>] path_openat+0x136f/0x4470 fs/namei.c:3406
 [<ffffffff814ccab1>] do_filp_open+0x1a1/0x270 fs/namei.c:3440
 [<ffffffff81495668>] do_sys_open+0x2f8/0x600 fs/open.c:1038
 [<ffffffff8149599d>] SYSC_open fs/open.c:1056 [inline]
 [<ffffffff8149599d>] SyS_open+0x2d/0x40 fs/open.c:1051
 [<ffffffff82718ba1>] entry_SYSCALL_64_fastpath+0x1e/0x9a
2 locks held by syz-executor.0/2114:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff8154e9cc>] __blkdev_get+0x10c/0xdf0 fs/block_dev.c:1199
 #1:  (loop_index_mutex){+.+.+.}, at: [<ffffffff81d3d70d>] lo_open+0x1d/0xb0 drivers/block/loop.c:1633
Sending NMI to all CPUs:
NMI backtrace for cpu 0
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.4.174+ #4
task: ffffffff82e151c0 task.stack: ffffffff82e00000
RIP: 0010:[<ffffffff812464fd>]  [<ffffffff812464fd>] arch_local_save_flags arch/x86/include/asm/paravirt.h:807 [inline]
RIP: 0010:[<ffffffff812464fd>]  [<ffffffff812464fd>] arch_local_irq_save arch/x86/include/asm/paravirt.h:829 [inline]
RIP: 0010:[<ffffffff812464fd>]  [<ffffffff812464fd>] rcu_idle_exit+0xd/0x100 kernel/rcu/tree.c:849
RSP: 0018:ffffffff82e07df0  EFLAGS: 00000286
RAX: 0000000000000286 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff81b0abec RDI: ffffffff8292c000
RBP: ffffffff82e07e08 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffffffff82e08000 R14: dffffc0000000000 R15: ffffffff82e00000
FS:  0000000000000000(0000) GS:ffff8801db600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000c42049f000 CR3: 00000001d748e000 CR4: 00000000001606b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff82e07e08 0000000000000000 0000000000000000 ffffffff82e07ed0
 ffffffff811eb811 ffffffff811eafe8 fffffbfff05c0001 ffffffff82e08000
 fffffbfff05c0001 ffffffff82e00008 ffffffff82e00008 0000000041b58ab3
Call Trace:
 [<ffffffff811eb811>] cpu_idle_poll kernel/sched/idle.c:67 [inline]
 [<ffffffff811eb811>] cpu_idle_loop kernel/sched/idle.c:251 [inline]
 [<ffffffff811eb811>] cpu_startup_entry+0x241/0x810 kernel/sched/idle.c:301
 [<ffffffff827055f9>] rest_init+0x190/0x199 init/main.c:410
 [<ffffffff831d58a0>] start_kernel+0x64a/0x67e init/main.c:682
 [<ffffffff831d430a>] x86_64_start_reservations+0x29/0x2b arch/x86/kernel/head64.c:196
 [<ffffffff831d4443>] x86_64_start_kernel+0x137/0x15a arch/x86/kernel/head64.c:185
Code: 23 00 e9 83 fa ff ff e8 e2 e9 23 00 e9 57 fa ff ff 0f 1f 00 66 2e 0f 1f 84 00 00 00 00 00 55 48 89 e5 41 54 53 48 83 ec 08 9c 58 <0f> 1f 44 00 00 49 89 c4 fa 66 0f 1f 44 00 00 e8 0f 25 fb ff 48 
NMI backtrace for cpu 1
CPU: 1 PID: 20 Comm: khungtaskd Not tainted 4.4.174+ #4
task: ffff8801da6c2f80 task.stack: ffff8800001e8000
RIP: 0010:[<ffffffff8109b617>]  [<ffffffff8109b617>] _flat_send_IPI_mask arch/x86/kernel/apic/apic_flat_64.c:62 [inline]
RIP: 0010:[<ffffffff8109b617>]  [<ffffffff8109b617>] flat_send_IPI_mask+0xf7/0x1b0 arch/x86/kernel/apic/apic_flat_64.c:69
RSP: 0018:ffff8800001efc88  EFLAGS: 00000046
RAX: 0000000000000000 RBX: 0000000000000c00 RCX: 0000000000000000
RDX: 0000000000000c00 RSI: 0000000000000000 RDI: ffffffffff5fc300
RBP: ffff8800001efcb8 R08: 0000000000000018 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000001 R12: 0000000000000246
R13: 0000000003000000 R14: ffffffff82e5f2e0 R15: 0000000000000002
FS:  0000000000000000(0000) GS:ffff8801db700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000625298 CR3: 00000000b2270000 CR4: 00000000001606b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 0000000000000001 ffffffff82e5f2e0 ffffffff831a6ac0 fffffbfff0634c34
 000000000001b6c0 0000000000000008 ffff8800001efcd8 ffffffff81092bee
 0000000000000008 ffffffff82924260 ffff8800001efd30 ffffffff81ab8252
Call Trace:
 [<ffffffff81092bee>] nmi_raise_cpu_backtrace+0x5e/0x80 arch/x86/kernel/apic/hw_nmi.c:33
 [<ffffffff81ab8252>] nmi_trigger_all_cpu_backtrace.cold+0xa1/0xae lib/nmi_backtrace.c:85
 [<ffffffff81092ca4>] arch_trigger_all_cpu_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
 [<ffffffff813b4762>] trigger_all_cpu_backtrace include/linux/nmi.h:44 [inline]
 [<ffffffff813b4762>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff813b4762>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff813b4762>] watchdog.cold+0xd3/0xee kernel/hung_task.c:238
 [<ffffffff811342c3>] kthread+0x273/0x310 kernel/kthread.c:211
 [<ffffffff82718fc5>] ret_from_fork+0x55/0x80 arch/x86/entry/entry_64.S:537
Code: 00 c3 5f ff 80 e6 10 75 e1 41 c1 e5 18 44 89 2c 25 10 c3 5f ff 44 89 fa 09 da 80 cf 04 41 83 ff 02 0f 44 d3 89 14 25 00 c3 5f ff <41> f7 c4 00 02 00 00 75 1e 4c 89 e7 57 9d 0f 1f 44 00 00 e8 f1