Buffer I/O error on dev loop3, logical block 9, lost async page write
INFO: task syz-executor3:17340 blocked for more than 120 seconds.
      Not tainted 4.9.94-g8683408 #4
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor3   D26536 17340   3891 0x00000006
 ffff88018f430000 0000000000000000 ffff8801cca89500 ffff8801d9b73000
 ffff8801db321b98 ffff8801d7b37390 ffffffff839e140d 0000000041b58ab3
 ffffffff841c03b8 ffffffff81234350 00ffffff8122e3c2 ffff8801db322468
Call Trace:
 [<ffffffff839e2a0f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839eee21>] schedule_timeout+0x861/0xf70 kernel/time/timer.c:1768
 [<ffffffff839e0bea>] io_schedule_timeout+0x1ba/0x390 kernel/sched/core.c:5180
 [<ffffffff839e3e59>] io_schedule include/linux/sched.h:460 [inline]
 [<ffffffff839e3e59>] bit_wait_io+0x19/0xa0 kernel/sched/wait.c:582
 [<ffffffff839e35a3>] __wait_on_bit+0x93/0x120 kernel/sched/wait.c:383
 [<ffffffff81431d70>] wait_on_page_bit+0x130/0x140 mm/filemap.c:802
 [<ffffffff81431f41>] wait_on_page_writeback include/linux/pagemap.h:526 [inline]
 [<ffffffff81431f41>] __filemap_fdatawait_range+0x1c1/0x290 mm/filemap.c:453
 [<ffffffff81432035>] filemap_fdatawait_range+0x25/0x50 mm/filemap.c:483
 [<ffffffff8143ac45>] filemap_fdatawait mm/filemap.c:533 [inline]
 [<ffffffff8143ac45>] filemap_write_and_wait+0xf5/0x130 mm/filemap.c:551
 [<ffffffff8162e186>] __sync_blockdev fs/block_dev.c:194 [inline]
 [<ffffffff8162e186>] sync_blockdev fs/block_dev.c:203 [inline]
 [<ffffffff8162e186>] __blkdev_put+0x1d6/0x840 fs/block_dev.c:1585
 [<ffffffff8162f5d5>] blkdev_put+0x85/0x560 fs/block_dev.c:1663
 [<ffffffff8162fb3b>] blkdev_close+0x8b/0xb0 fs/block_dev.c:1670
 [<ffffffff815759d3>] __fput+0x263/0x700 fs/file_table.c:208
 [<ffffffff81575ef5>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8119600c>] task_work_run+0x10c/0x180 kernel/task_work.c:116
 [<ffffffff8113ec91>] exit_task_work include/linux/task_work.h:21 [inline]
 [<ffffffff8113ec91>] do_exit+0x9e1/0x27c0 kernel/exit.c:837
 [<ffffffff81144d91>] do_group_exit+0x111/0x340 kernel/exit.c:941
 [<ffffffff81167b5f>] get_signal+0x4cf/0x1450 kernel/signal.c:2317
 [<ffffffff810524d7>] do_signal+0x87/0x19f0 arch/x86/kernel/signal.c:807
 [<ffffffff81005581>] exit_to_usermode_loop+0xe1/0x120 arch/x86/entry/common.c:157
 [<ffffffff810064d4>] prepare_exit_to_usermode arch/x86/entry/common.c:191 [inline]
 [<ffffffff810064d4>] syscall_return_slowpath arch/x86/entry/common.c:260 [inline]
 [<ffffffff810064d4>] do_syscall_64+0x364/0x490 arch/x86/entry/common.c:287
 [<ffffffff839f2313>] 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: [<ffffffff813646bc>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff813646bc>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81423bb0>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3778:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f04b2>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff8211c622>] n_tty_read+0x202/0x16b0 drivers/tty/n_tty.c:2133
3 locks held by kworker/u4:2/25638:
 #0:  ("writeback"){++++.+}, at: [<ffffffff8118ad0e>] work_static include/linux/workqueue.h:186 [inline]
 #0:  ("writeback"){++++.+}, at: [<ffffffff8118ad0e>] set_work_data kernel/workqueue.c:617 [inline]
 #0:  ("writeback"){++++.+}, at: [<ffffffff8118ad0e>] set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
 #0:  ("writeback"){++++.+}, at: [<ffffffff8118ad0e>] process_one_work+0x6ee/0x1500 kernel/workqueue.c:2085
 #1:  ((&(&wb->dwork)->work)){+.+.+.}, at: [<ffffffff8118ad48>] process_one_work+0x728/0x1500 kernel/workqueue.c:2089
 #2:  (&type->s_umount_key#29){++++..}, at: [<ffffffff81579e90>] trylock_super+0x20/0xf0 fs/super.c:393
1 lock held by syz-executor3/17340:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff8162e06b>] __blkdev_put+0xbb/0x840 fs/block_dev.c:1579
1 lock held by blkid/17412:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff8162e8fc>] __blkdev_get+0x10c/0xd60 fs/block_dev.c:1268

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

NMI backtrace for cpu 0
CPU: 0 PID: 519 Comm: khungtaskd Not tainted 4.9.94-g8683408 #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d871fd08 ffffffff81eb0aa9 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b7d60 ffff8801d871fd40
 ffffffff81ebbdd7 0000000000000000 0000000000000000 0000000000000002
Call Trace:
 [<ffffffff81eb0aa9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb0aa9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebbdd7>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebbd6a>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b7e64>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81364c54>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81364c54>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81364c54>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81364c54>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119ad2d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f24dc>] 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 skipped: idling at pc 0xffffffff839f0f16