INFO: task syz-executor0:8834 blocked for more than 120 seconds.
      Not tainted 4.9.98-g63a812b #20
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor0   D28024  8834   3870 0x00000004
 ffff8801cdafc800 0000000000000000 ffff8801cd1824c0 ffff8801d9a6b000
 ffff8801db321b98 ffff8801d40cf680 ffffffff839e377d 0000000041b58ab3
 ffffffff843c0f58 ffffffff81234380 00ff880100000001 ffff8801db322468
Call Trace:
 [<ffffffff839e4d7f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839f1191>] schedule_timeout+0x861/0xf70 kernel/time/timer.c:1768
 [<ffffffff839e2f5a>] io_schedule_timeout+0x1ba/0x390 kernel/sched/core.c:5180
 [<ffffffff839e66b3>] do_wait_for_common kernel/sched/completion.c:75 [inline]
 [<ffffffff839e66b3>] __wait_for_common kernel/sched/completion.c:93 [inline]
 [<ffffffff839e66b3>] wait_for_common_io kernel/sched/completion.c:107 [inline]
 [<ffffffff839e66b3>] wait_for_completion_io+0x203/0x2e0 kernel/sched/completion.c:155
 [<ffffffff81df8682>] submit_bio_wait+0x112/0x180 block/bio.c:885
 [<ffffffff81e2add2>] blkdev_issue_flush+0x152/0x220 block/blk-flush.c:518
 [<ffffffff8162c6f5>] blkdev_fsync+0x85/0xb0 fs/block_dev.c:378
 [<ffffffff81617cfc>] vfs_fsync_range+0x10c/0x260 fs/sync.c:195
 [<ffffffff81617e79>] vfs_fsync+0x29/0x30 fs/sync.c:209
 [<ffffffff825c3ba2>] __loop_update_dio+0x452/0x5d0 drivers/block/loop.c:207
 [<ffffffff825c77de>] loop_set_dio drivers/block/loop.c:1330 [inline]
 [<ffffffff825c77de>] lo_ioctl+0x1ae/0x1aa0 drivers/block/loop.c:1384
 [<ffffffff81e54a86>] __blkdev_driver_ioctl block/ioctl.c:294 [inline]
 [<ffffffff81e54a86>] blkdev_ioctl+0x7b6/0x1a70 block/ioctl.c:590
 [<ffffffff816301ee>] block_ioctl+0xde/0x120 fs/block_dev.c:1688
 [<ffffffff815b03dc>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815b03dc>] file_ioctl fs/ioctl.c:493 [inline]
 [<ffffffff815b03dc>] do_vfs_ioctl+0x1ac/0x11a0 fs/ioctl.c:677
 [<ffffffff815b145f>] SYSC_ioctl fs/ioctl.c:694 [inline]
 [<ffffffff815b145f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f4653>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb

Showing all locks held in the system:
2 locks held by khungtaskd/520:
 #0:  (rcu_read_lock){......}, at: [<ffffffff813646ec>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff813646ec>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81423ba0>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3775:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f2822>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8211cbb2>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2133
1 lock held by syz-executor0/8834:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825c76bb>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor0/8835:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825c76bb>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
1 lock held by syz-executor0/8836:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825c76bb>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344

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

NMI backtrace for cpu 0
CPU: 0 PID: 520 Comm: khungtaskd Not tainted 4.9.98-g63a812b #20
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d8477d08 ffffffff81eb0e89 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b7da0 ffff8801d8477d40
 ffffffff81ebc187 0000000000000000 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb0e89>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb0e89>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebc187>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebc11a>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b7ea4>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81364c84>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81364c84>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81364c84>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81364c84>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119ad5d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f481c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 3677 Comm: rs:main Q:Reg Not tainted 4.9.98-g63a812b #20
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801b978e000 task.stack: ffff8801b9638000
RIP: 0010:[<ffffffff811b92da>] 
c [<ffffffff811b92da>] __might_sleep+0x3a/0x1a0 kernel/sched/core.c:7942
RSP: 0018:ffff8801b963f3d0  EFLAGS: 00000246
RAX: dffffc0000000000 RBX: ffff8801b978e000 RCX: 0000000000000001
RDX: 1ffff100372f1c02 RSI: 0000000000000189 RDI: ffff8801b978e010
RBP: ffff8801b963f400 R08: 0000000000000000 R09: 0000000000000001
R10: ffff8801b978e000 R11: 0000000000000001 R12: ffffffff843c4d87
R13: 0000000000000189 R14: 0000000000000000 R15: ffffffff81620372
FS:  00007f44dbe03700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000117a000 CR3: 00000001c4030000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff81234380
c ffffffff815386c7
c 0000000000400000
c ffff8801d9905500
c
 0000000000001000
c 0000000002408040
c ffff8801b963f440
c ffffffff81534612
c
 ffffffff8143b602
c 0000000002400040
c 0000000000000000
c 0000000000001000
c
Call Trace:
 [<ffffffff81534612>] slab_pre_alloc_hook mm/slab.h:393 [inline]
 [<ffffffff81534612>] slab_alloc_node mm/slub.c:2641 [inline]
 [<ffffffff81534612>] slab_alloc mm/slub.c:2723 [inline]
 [<ffffffff81534612>] kmem_cache_alloc+0x112/0x290 mm/slub.c:2728
 [<ffffffff81620372>] kmem_cache_zalloc include/linux/slab.h:626 [inline]
 [<ffffffff81620372>] alloc_buffer_head+0x22/0xd0 fs/buffer.c:3383
 [<ffffffff81620587>] alloc_page_buffers+0xb7/0x200 fs/buffer.c:875
 [<ffffffff81620dd9>] create_empty_buffers+0x39/0x470 fs/buffer.c:1582
 [<ffffffff81621364>] create_page_buffers+0x154/0x1c0 fs/buffer.c:1657
 [<ffffffff81627251>] __block_write_begin_int+0x1b1/0x1040 fs/buffer.c:1966
 [<ffffffff81628110>] __block_write_begin+0x30/0x40 fs/buffer.c:2038
 [<ffffffff8175390d>] ext4_da_write_begin+0x2ed/0x1020 fs/ext4/inode.c:3004
 [<ffffffff81433b71>] generic_perform_write+0x301/0x510 mm/filemap.c:2740
 [<ffffffff8143b602>] __generic_file_write_iter+0x352/0x540 mm/filemap.c:2865
 [<ffffffff8172a063>] ext4_file_write_iter+0x463/0xd90 fs/ext4/file.c:165
 [<ffffffff8156c3a0>] new_sync_write fs/read_write.c:496 [inline]
 [<ffffffff8156c3a0>] __vfs_write+0x3e0/0x580 fs/read_write.c:509
 [<ffffffff81570197>] vfs_write+0x187/0x530 fs/read_write.c:557
 [<ffffffff81573fc9>] SYSC_write fs/read_write.c:604 [inline]
 [<ffffffff81573fc9>] SyS_write+0xd9/0x1c0 fs/read_write.c:596
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f4653>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 
c56 
c41 
c89 
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c41 
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c89 
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c41 
c54 
c49 
c89 
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c53 
c65 
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c01 
c00 
c48 
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c10 
c48 
c83 
cec 
c10 
c48 
c89 
cfa 
c48 
cc1 
cea 
c03 
c80 
c3c 
c02 
c00 
c<0f> 
c85 
c18 
c01 
c00 
c00 
c48 
c8b 
c43 
c10 
c48 
c85 
cc0 
c74 
c3e 
c65 
c48 
c8b 
c1c 
c25 
c40 
c