Buffer I/O error on dev loop0, logical block 27, async page read
Buffer I/O error on dev loop0, logical block 28, async page read
Buffer I/O error on dev loop0, logical block 29, async page read
Buffer I/O error on dev loop0, logical block 30, async page read
Buffer I/O error on dev loop0, logical block 31, async page read
INFO: task syz-executor2:13012 blocked for more than 120 seconds.
      Not tainted 4.9.87-gd6f2774 #5
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor2   D28944 13012   6262 0x20020004
 ffff8801d4a59800 0000000000000000 ffff8801d7af1f80 ffff8801d6946000
 ffff8801db221b98 ffff8801b21f7930 ffffffff838a5adb 0000000041b58ab3
 ffffffff84193ea8 00ffffff8123c1a0 ffff8801db222468 ffff8801db222490
Call Trace:
 [<ffffffff838a707f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3550
 [<ffffffff838b31dc>] schedule_timeout+0x56c/0x10b0 kernel/time/timer.c:1768
 [<ffffffff838a528e>] io_schedule_timeout+0x1be/0x390 kernel/sched/core.c:5172
 [<ffffffff838a84f9>] io_schedule include/linux/sched.h:460 [inline]
 [<ffffffff838a84f9>] bit_wait_io+0x19/0xa0 kernel/sched/wait.c:582
 [<ffffffff838a7bd7>] __wait_on_bit+0x57/0x120 kernel/sched/wait.c:383
 [<ffffffff81432874>] wait_on_page_bit+0xf4/0x140 mm/filemap.c:802
 [<ffffffff81432a81>] wait_on_page_writeback include/linux/pagemap.h:526 [inline]
 [<ffffffff81432a81>] __filemap_fdatawait_range+0x1c1/0x2b0 mm/filemap.c:453
 [<ffffffff8143c9e3>] filemap_fdatawait_keep_errors+0x63/0x80 mm/filemap.c:511
 [<ffffffff81616490>] fdatawait_one_bdev+0x50/0x70 fs/sync.c:94
 [<ffffffff81631b49>] iterate_bdevs+0x109/0x260 fs/block_dev.c:1978
 [<ffffffff81616d61>] sys_sync+0xe1/0x170 fs/sync.c:116
 [<ffffffff81006f95>] do_syscall_32_irqs_on arch/x86/entry/common.c:325 [inline]
 [<ffffffff81006f95>] do_fast_syscall_32+0x2f5/0x870 arch/x86/entry/common.c:387
 [<ffffffff838b8250>] entry_SYSENTER_compat+0x90/0xa2 arch/x86/entry/entry_64_compat.S:137

Showing all locks held in the system:
3 locks held by kworker/u4:2/191:
 #0:  ("writeback"){.+.+.+}, at: [<ffffffff81189922>] work_static include/linux/workqueue.h:186 [inline]
 #0:  ("writeback"){.+.+.+}, at: [<ffffffff81189922>] set_work_data kernel/workqueue.c:617 [inline]
 #0:  ("writeback"){.+.+.+}, at: [<ffffffff81189922>] set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
 #0:  ("writeback"){.+.+.+}, at: [<ffffffff81189922>] process_one_work+0x6f2/0x1610 kernel/workqueue.c:2085
 #1:  ((&(&wb->dwork)->work)){+.+.+.}, at: [<ffffffff8118995c>] process_one_work+0x72c/0x1610 kernel/workqueue.c:2089
 #2:  (&type->s_umount_key#22){.+.+..}, at: [<ffffffff8157a160>] trylock_super+0x20/0x100 fs/super.c:393
2 locks held by khungtaskd/514:
 #0:  (rcu_read_lock){......}, at: [<ffffffff81373315>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff81373315>] watchdog+0x125/0xa70 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81238300>] debug_show_all_locks+0x70/0x280 kernel/locking/lockdep.c:4336
2 locks held by getty/3779:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838b4d52>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff8200b0d4>] n_tty_read+0x1f4/0x16c0 drivers/tty/n_tty.c:2133
1 lock held by blkid/11721:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff8162f6ca>] blkdev_put+0x2a/0x550 fs/block_dev.c:1621
1 lock held by syz-executor2/13012:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff81631b08>] iterate_bdevs+0xc8/0x260 fs/block_dev.c:1976
1 lock held by syz-executor2/13017:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff81631b08>] iterate_bdevs+0xc8/0x260 fs/block_dev.c:1976

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

NMI backtrace for cpu 0
CPU: 0 PID: 514 Comm: khungtaskd Not tainted 4.9.87-gd6f2774 #5
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d85f7d00 ffffffff81d95bd9 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810bb230 ffff8801d85f7d38
 ffffffff81da0cfd 0000000000000000 0000000000000000 ffff8801d321b418
Call Trace:
 [<ffffffff81d95bd9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d95bd9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81da0cfd>] nmi_cpu_backtrace+0xfd/0x120 lib/nmi_backtrace.c:99
 [<ffffffff81da0e37>] nmi_trigger_cpumask_backtrace+0x117/0x190 lib/nmi_backtrace.c:60
 [<ffffffff810bb324>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff813738e0>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff813738e0>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff813738e0>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff813738e0>] watchdog+0x6f0/0xa70 kernel/hung_task.c:239
 [<ffffffff8119a92d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838b6cec>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:374
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at pc 0xffffffff838b57c6