INFO: task syz-executor0:22546 blocked for more than 120 seconds.
      Not tainted 4.9.109-ge1815b3 #52
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor0   D28872 22546   3825 0x00000004
 ffff88019b9bc800 ffff8801bb139a40 ffff8801bb139a40 ffff880189598000
 ffff8801db321c18 ffff8801bf8b79f0 ffffffff839e8a8d 0000000000000002
 0000000041b58ab3 ffffffff843b9d9b 00ffffff81221500 ffff8801db3224e8
Call Trace:
 [<ffffffff839ea08f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff81e41524>] blk_mq_freeze_queue_wait+0x114/0x230 block/blk-mq.c:75
 [<ffffffff81e4a81d>] blk_freeze_queue block/blk-mq.c:92 [inline]
 [<ffffffff81e4a81d>] blk_mq_freeze_queue+0x1d/0x20 block/blk-mq.c:101
 [<ffffffff825caf12>] loop_switch drivers/block/loop.c:599 [inline]
 [<ffffffff825caf12>] loop_change_fd drivers/block/loop.c:685 [inline]
 [<ffffffff825caf12>] lo_ioctl+0x722/0x1aa0 drivers/block/loop.c:1350
 [<ffffffff81e57a26>] __blkdev_driver_ioctl block/ioctl.c:294 [inline]
 [<ffffffff81e57a26>] blkdev_ioctl+0x7b6/0x1a70 block/ioctl.c:590
 [<ffffffff81632b8e>] block_ioctl+0xde/0x120 fs/block_dev.c:1688
 [<ffffffff815b2b9c>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815b2b9c>] file_ioctl fs/ioctl.c:493 [inline]
 [<ffffffff815b2b9c>] do_vfs_ioctl+0x1ac/0x11a0 fs/ioctl.c:677
 [<ffffffff815b3c1f>] SYSC_ioctl fs/ioctl.c:694 [inline]
 [<ffffffff815b3c1f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f9993>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb

Showing all locks held in the system:
2 locks held by khungtaskd/519:
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136662c>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136662c>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81425cb7>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3773:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f7b32>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff8211fce2>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2133
1 lock held by syz-executor0/22546:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor0/22555:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor0/22561:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by blkid/22688:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344

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

NMI backtrace for cpu 1
CPU: 1 PID: 519 Comm: khungtaskd Not tainted 4.9.109-ge1815b3 #52
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d85bfd08 ffffffff81eb3e29 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810b9580 ffff8801d85bfd40
 ffffffff81ebf127 0000000000000001 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb3e29>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb3e29>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebf127>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebf0ba>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b9684>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81366bc4>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81366bc4>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81366bc4>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81366bc4>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119d04d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f9b5c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 3675 Comm: rs:main Q:Reg Not tainted 4.9.109-ge1815b3 #52
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801b9060000 task.stack: ffff8801b9398000
RIP: 0010:[<ffffffff8122fbd0>] 
c [<ffffffff8122fbd0>] match_held_lock+0x10/0x570 kernel/locking/lockdep.c:3404
RSP: 0018:ffff8801db207c90  EFLAGS: 00000006
RAX: dffffc0000000000 RBX: ffff8801b9060000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff846def20 RDI: ffff8801b9060918
RBP: ffff8801db207c98 R08: ffff8801b9060988 R09: 0000000000000001
R10: ffff8801b9060000 R11: 1ffff1003720c12c R12: ffffed003720c118
R13: ffff8801b90608c8 R14: ffffffff846def20 R15: 0000000000000002
FS:  00007fda28d71700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000017ca000 CR3: 00000001d8324000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 0000000000000002
c ffff8801db207cd8
c ffffffff812301d2
c ffff8801b90608c0
c
 0000000000000246
c ffff8801b9060000
c ffffffff846def20
c 0000000000000100
c
 dffffc0000000000
c ffff8801db207d00
c ffffffff81230a04
c 0000000000000003
c
Call Trace:
 <IRQ> 
d [<ffffffff812301d2>] __lock_is_held+0xa2/0xf0 kernel/locking/lockdep.c:3597
 [<ffffffff81230a04>] lock_is_held+0xb4/0x140 kernel/locking/lockdep.c:3794
 [<ffffffff8127c053>] rcu_read_lock_sched_held+0x103/0x120 kernel/rcu/update.c:112
 [<ffffffff812989e2>] trace_timer_expire_entry include/trace/events/timer.h:79 [inline]
 [<ffffffff812989e2>] call_timer_fn+0x252/0x6e0 kernel/time/timer.c:1318
 [<ffffffff8129fa57>] expire_timers kernel/time/timer.c:1359 [inline]
 [<ffffffff8129fa57>] __run_timers kernel/time/timer.c:1658 [inline]
 [<ffffffff8129fa57>] run_timer_softirq+0x1047/0x1590 kernel/time/timer.c:1684
 [<ffffffff83a0057b>] __do_softirq+0x20b/0x937 kernel/softirq.c:284
 [<ffffffff8114b227>] invoke_softirq kernel/softirq.c:364 [inline]
 [<ffffffff8114b227>] irq_exit+0x147/0x190 kernel/softirq.c:405
 [<ffffffff839ff161>] exiting_irq arch/x86/include/asm/apic.h:659 [inline]
 [<ffffffff839ff161>] smp_apic_timer_interrupt+0x81/0xa0 arch/x86/kernel/apic/apic.c:960
 [<ffffffff839fb2f0>] apic_timer_interrupt+0xa0/0xb0 arch/x86/entry/entry_64.S:648
 <EOI> 
d [<ffffffff8105a768>] ? in_task_stack+0x28/0x40 arch/x86/kernel/dumpstack.c:39
 [<ffffffff810d2f55>] __unwind_start+0xe5/0x3c0 arch/x86/kernel/unwind_frame.c:79
 [<ffffffff8107b899>] unwind_start arch/x86/include/asm/unwind.h:39 [inline]
 [<ffffffff8107b899>] __save_stack_trace+0x59/0xf0 arch/x86/kernel/stacktrace.c:41
 [<ffffffff8107b946>] save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
 [<ffffffff8153aa73>] save_stack+0x43/0xd0 mm/kasan/kasan.c:505
 [<ffffffff8153ae57>] set_track mm/kasan/kasan.c:517 [inline]
 [<ffffffff8153ae57>] kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:609
 [<ffffffff8153b422>] kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:547
 [<ffffffff81536d4e>] slab_post_alloc_hook mm/slab.h:417 [inline]
 [<ffffffff81536d4e>] slab_alloc_node mm/slub.c:2715 [inline]
 [<ffffffff81536d4e>] slab_alloc mm/slub.c:2723 [inline]
 [<ffffffff81536d4e>] kmem_cache_alloc+0xbe/0x290 mm/slub.c:2728
 [<ffffffff81622d12>] kmem_cache_zalloc include/linux/slab.h:626 [inline]
 [<ffffffff81622d12>] alloc_buffer_head+0x22/0xd0 fs/buffer.c:3383
 [<ffffffff81622f27>] alloc_page_buffers+0xb7/0x200 fs/buffer.c:875
 [<ffffffff81623779>] create_empty_buffers+0x39/0x470 fs/buffer.c:1582
 [<ffffffff81623d04>] create_page_buffers+0x154/0x1c0 fs/buffer.c:1657
 [<ffffffff81629bf1>] __block_write_begin_int+0x1b1/0x1040 fs/buffer.c:1966
 [<ffffffff8162aab0>] __block_write_begin+0x30/0x40 fs/buffer.c:2038
 [<ffffffff817567dd>] ext4_da_write_begin+0x2ed/0x1020 fs/ext4/inode.c:3004
 [<ffffffff81435c91>] generic_perform_write+0x301/0x510 mm/filemap.c:2740
 [<ffffffff8143d722>] __generic_file_write_iter+0x352/0x540 mm/filemap.c:2865
 [<ffffffff8172cf33>] ext4_file_write_iter+0x463/0xd90 fs/ext4/file.c:165
 [<ffffffff8156eb60>] new_sync_write fs/read_write.c:496 [inline]
 [<ffffffff8156eb60>] __vfs_write+0x3e0/0x580 fs/read_write.c:509
 [<ffffffff81572957>] vfs_write+0x187/0x530 fs/read_write.c:557
 [<ffffffff81576789>] SYSC_write fs/read_write.c:604 [inline]
 [<ffffffff81576789>] SyS_write+0xd9/0x1c0 fs/read_write.c:596
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f9993>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 
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c