Buffer I/O error on dev loop0, logical block 7, lost async page write
Buffer I/O error on dev loop0, logical block 8, lost async page write
Buffer I/O error on dev loop0, logical block 9, lost async page write
buffer_io_error: 119 callbacks suppressed
Buffer I/O error on dev loop0, logical block 8176, async page read
INFO: task syz-executor2:18544 blocked for more than 120 seconds.
      Not tainted 4.9.94-g8683408 #3
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor2   D28264 18544   3841 0x00000004
 ffff8801d7674800 ffff8801b9ccd500 ffff8801b98b8540 ffff8801a1610000
 ffff8801db221b98 ffff88019cbcf940 ffffffff838c040d 1ffff10033979f1c
 ffffffff85351d98 0000000041b58ab3 00ffffff841a49d8 ffff8801db222468
Call Trace:
 [<ffffffff838c1a0f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff838cde21>] schedule_timeout+0x861/0xf70 kernel/time/timer.c:1768
 [<ffffffff838bfbea>] io_schedule_timeout+0x1ba/0x390 kernel/sched/core.c:5180
 [<ffffffff838c2e59>] io_schedule include/linux/sched.h:460 [inline]
 [<ffffffff838c2e59>] bit_wait_io+0x19/0xa0 kernel/sched/wait.c:582
 [<ffffffff838c25a3>] __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
 [<ffffffff8143be63>] filemap_fdatawait_keep_errors+0x63/0x80 mm/filemap.c:511
 [<ffffffff81617a60>] fdatawait_one_bdev+0x50/0x70 fs/sync.c:94
 [<ffffffff81632f5c>] iterate_bdevs+0x10c/0x260 fs/block_dev.c:1978
 [<ffffffff81618341>] sys_sync+0xe1/0x170 fs/sync.c:116
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff838d1313>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb

Showing all locks held in the system:
2 locks held by khungtaskd/515:
 #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/3741:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838cf4b2>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff82007082>] n_tty_read+0x202/0x16b0 drivers/tty/n_tty.c:2133
3 locks held by kworker/u4:9/8529:
 #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 blkid/16920:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff8162f57a>] blkdev_put+0x2a/0x560 fs/block_dev.c:1621
1 lock held by syz-executor2/18544:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff81632f18>] iterate_bdevs+0xc8/0x260 fs/block_dev.c:1976
1 lock held by syz-executor2/18565:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff81632f18>] iterate_bdevs+0xc8/0x260 fs/block_dev.c:1976

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

NMI backtrace for cpu 1
CPU: 1 PID: 515 Comm: khungtaskd Not tainted 4.9.94-g8683408 #3
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d855fd08 ffffffff81d9b509 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810b7d60 ffff8801d855fd40
 ffffffff81da6837 0000000000000001 0000000000000000 0000000000000002
Call Trace:
 [<ffffffff81d9b509>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d9b509>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81da6837>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81da67ca>] 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
 [<ffffffff838d14dc>] 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 skipped: idling at pc 0xffffffff838cff16