INFO: task syz-executor6:5914 blocked for more than 120 seconds.
      Not tainted 4.9.78-gf518fe4 #22
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor6   D29936  5914   3430 0x00000004
 ffff8801c1b4e000 ffff8801c1cbaa00 ffff8801c1cb9a40 ffff8801c1a49800
 ffff8801db221b98 ffff8801c158fa40 ffffffff838a1bbb 0000000000000002
 0000000041b58ab3 00ffffff8418af54 ffff8801db222468 ffff8801db222490
Call Trace:
 [<ffffffff838a315f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3550
 [<ffffffff81d216e4>] blk_mq_freeze_queue_wait+0x114/0x230 block/blk-mq.c:75
 [<ffffffff81d2a79d>] blk_freeze_queue block/blk-mq.c:92 [inline]
 [<ffffffff81d2a79d>] blk_mq_freeze_queue+0x1d/0x20 block/blk-mq.c:101
 [<ffffffff824b709f>] loop_switch drivers/block/loop.c:599 [inline]
 [<ffffffff824b709f>] loop_change_fd drivers/block/loop.c:682 [inline]
 [<ffffffff824b709f>] lo_ioctl+0xfdf/0x1990 drivers/block/loop.c:1343
 [<ffffffff81d374fa>] __blkdev_driver_ioctl block/ioctl.c:294 [inline]
 [<ffffffff81d374fa>] blkdev_ioctl+0x4aa/0x1a60 block/ioctl.c:590
 [<ffffffff8162be8e>] block_ioctl+0xde/0x120 fs/block_dev.c:1688
 [<ffffffff815adfaa>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815adfaa>] do_vfs_ioctl+0x1aa/0x1140 fs/ioctl.c:679
 [<ffffffff815aefcf>] SYSC_ioctl fs/ioctl.c:694 [inline]
 [<ffffffff815aefcf>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff838b2c6e>] entry_SYSCALL_64_fastpath+0x29/0xe8

Showing all locks held in the system:
2 locks held by khungtaskd/513:
 #0:  (rcu_read_lock){......}, at: [<ffffffff81372df5>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff81372df5>] watchdog+0x125/0xa70 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81237f80>] debug_show_all_locks+0x70/0x280 kernel/locking/lockdep.c:4336
2 locks held by getty/3323:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838b0e32>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff820096f4>] n_tty_read+0x1f4/0x16c0 drivers/tty/n_tty.c:2133
1 lock held by syz-executor6/5914:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff824b614f>] lo_ioctl+0x8f/0x1990 drivers/block/loop.c:1337

=============================================

NMI backtrace for cpu 1
CPU: 1 PID: 513 Comm: khungtaskd Not tainted 4.9.78-gf518fe4 #22
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d8b17d00 ffffffff81d943a9 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810bac10 ffff8801d8b17d38
 ffffffff81d9f4cd 0000000000000001 0000000000000000 ffff8801c1fde418
Call Trace:
 [<ffffffff81d943a9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d943a9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81d9f4cd>] nmi_cpu_backtrace+0xfd/0x120 lib/nmi_backtrace.c:99
 [<ffffffff81d9f607>] nmi_trigger_cpumask_backtrace+0x117/0x190 lib/nmi_backtrace.c:60
 [<ffffffff810bad04>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff813733c0>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff813733c0>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff813733c0>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff813733c0>] watchdog+0x6f0/0xa70 kernel/hung_task.c:239
 [<ffffffff8119a72d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838b2fdc>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:477
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.9.78-gf518fe4 #22
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffffffff84429880 task.stack: ffffffff84400000
RIP: 0010:[<ffffffff838b74a6>] 
c [<ffffffff838b74a6>] apic_eoi arch/x86/include/asm/apic.h:403 [inline]
RIP: 0010:[<ffffffff838b74a6>] 
c [<ffffffff838b74a6>] ack_APIC_irq arch/x86/include/asm/apic.h:447 [inline]
RIP: 0010:[<ffffffff838b74a6>] 
c [<ffffffff838b74a6>] smp_reschedule_interrupt+0x26/0x80 arch/x86/kernel/smp.c:265
RSP: 0018:ffff8801db207fe0  EFLAGS: 00000046
RAX: dffffc0000000000 RBX: ffffffff84a27968 RCX: 0000000000000000
RDX: 1ffffffff083ff04 RSI: 0000000000000000 RDI: ffffffff841ff820
RBP: ffff8801db207fe8 R08: 0000000000000001 R09: ffff88021fffd008
R10: ffff88021fffd018 R11: ffff88021fffd010 R12: 0000000000000000
R13: ffffffff84a36a78 R14: 0000000000000000 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f63275279b8 CR3: 00000001cc552000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff84a27968
c ffffffff84407dc0
c ffffffff838b5100
c ffffffff84407d18
c <EOI> 
c
 0000000000000000
c 0000000000000000
c ffffffff84a36a78
c 0000000000000000
c
 ffffffff84407dc0
c ffffffff84a27968
c 0000000000000000
c 0000000000000000
c
Call Trace:
 <IRQ> 
d [<ffffffff838b5100>] reschedule_interrupt+0xa0/0xb0 arch/x86/entry/entry_64.S:775
 <EOI> 
d [<ffffffff838b18a6>] ? native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:53
 [<ffffffff838b0ed5>] arch_safe_halt arch/x86/include/asm/paravirt.h:103 [inline]
 [<ffffffff838b0ed5>] default_idle+0x55/0x360 arch/x86/kernel/process.c:295
 [<ffffffff8106bc9a>] arch_cpu_idle+0xa/0x10 arch/x86/kernel/process.c:286
 [<ffffffff838b1ce6>] default_idle_call+0x36/0x60 kernel/sched/idle.c:97
 [<ffffffff81226580>] cpuidle_idle_call kernel/sched/idle.c:155 [inline]
 [<ffffffff81226580>] cpu_idle_loop kernel/sched/idle.c:248 [inline]
 [<ffffffff81226580>] cpu_startup_entry+0x2b0/0x380 kernel/sched/idle.c:303
 [<ffffffff8389e804>] rest_init+0x184/0x190 init/main.c:408
 [<ffffffff84a6f8b6>] start_kernel+0x688/0x6bd init/main.c:663
 [<ffffffff84a6e29d>] x86_64_start_reservations+0x2a/0x2c arch/x86/kernel/head64.c:196
 [<ffffffff84a6e3df>] x86_64_start_kernel+0x140/0x163 arch/x86/kernel/head64.c:177
Code: 
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c<75> 
c46 
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c