b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
__find_get_block_slow() failed. block=1, b_blocknr=8
b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
INFO: task syz-executor0:3872 blocked for more than 140 seconds.
      Not tainted 4.9.122-g54068d6 #26
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor0   D26872  3872      1 0x00000004
 ffff8801d9aec800 ffff8801d4fd2f40 ffff8801da0e2f40 ffff880197984800
 ffff8801db321c18 ffff8801a7427b40 ffffffff839efdcd 0000000000000002
 0000000041b58ab3 ffffffff843bbbe4 00ffffff81223830 ffff8801db3224e8
Call Trace:
 [<ffffffff839f13cf>] schedule+0x7f/0x1b0 kernel/sched/core.c:3553
 [<ffffffff81606739>] wb_wait_for_completion+0x149/0x1b0 fs/fs-writeback.c:221
 [<ffffffff816069a7>] __writeback_inodes_sb_nr+0x207/0x300 fs/fs-writeback.c:2310
 [<ffffffff81606af7>] writeback_inodes_sb_nr fs/fs-writeback.c:2327 [inline]
 [<ffffffff81606af7>] writeback_inodes_sb+0x27/0x30 fs/fs-writeback.c:2342
 [<ffffffff8161e6b3>] __sync_filesystem fs/sync.c:35 [inline]
 [<ffffffff8161e6b3>] sync_filesystem+0x93/0x240 fs/sync.c:63
 [<ffffffff8157d125>] generic_shutdown_super+0x75/0x300 fs/super.c:423
 [<ffffffff8157da5f>] kill_block_super+0x9f/0x120 fs/super.c:1127
 [<ffffffff8157ddd5>] deactivate_locked_super+0x75/0xd0 fs/super.c:310
 [<ffffffff8157e7e1>] deactivate_super+0x91/0xd0 fs/super.c:341
 [<ffffffff815e09f2>] cleanup_mnt+0xb2/0x160 fs/namespace.c:1143
 [<ffffffff815e0b26>] __cleanup_mnt+0x16/0x20 fs/namespace.c:1150
 [<ffffffff8119a62c>] task_work_run+0x10c/0x180 kernel/task_work.c:116
 [<ffffffff8100559c>] tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 [<ffffffff8100559c>] exit_to_usermode_loop+0xfc/0x120 arch/x86/entry/common.c:161
 [<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
 [<ffffffff83a00cd3>] 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: [<ffffffff81368a5c>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff81368a5c>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff814282c8>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by rs:main Q:Reg/3676:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<ffffffff815dbb4c>] __fdget_pos+0xac/0xd0 fs/file.c:781
 #1:  (sb_writers#3){.+.+.+}, at: [<ffffffff815767be>] file_start_write include/linux/fs.h:2640 [inline]
 #1:  (sb_writers#3){.+.+.+}, at: [<ffffffff815767be>] vfs_write+0x3ae/0x530 fs/read_write.c:556
2 locks held by getty/3774:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839fee72>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff82124562>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2142
1 lock held by syz-executor0/3872:
 #0:  (&type->s_umount_key#41){++++..}, at: [<ffffffff8157e7d9>] deactivate_super+0x89/0xd0 fs/super.c:340
1 lock held by init/11069:
 #0:  (tty_mutex){+.+.+.}, at: [<ffffffff8211e96c>] tty_open_by_driver drivers/tty/tty_io.c:2047 [inline]
 #0:  (tty_mutex){+.+.+.}, at: [<ffffffff8211e96c>] tty_open+0x46c/0xe20 drivers/tty/tty_io.c:2125
1 lock held by init/11070:
 #0:  (tty_mutex){+.+.+.}, at: [<ffffffff8211e96c>] tty_open_by_driver drivers/tty/tty_io.c:2047 [inline]
 #0:  (tty_mutex){+.+.+.}, at: [<ffffffff8211e96c>] tty_open+0x46c/0xe20 drivers/tty/tty_io.c:2125
1 lock held by init/11071:
 #0:  (tty_mutex){+.+.+.}, at: [<ffffffff8211e96c>] tty_open_by_driver drivers/tty/tty_io.c:2047 [inline]
 #0:  (tty_mutex){+.+.+.}, at: [<ffffffff8211e96c>] tty_open+0x46c/0xe20 drivers/tty/tty_io.c:2125
1 lock held by init/11072:
 #0:  (tty_mutex){+.+.+.}, at: [<ffffffff8211e96c>] tty_open_by_driver drivers/tty/tty_io.c:2047 [inline]
 #0:  (tty_mutex){+.+.+.}, at: [<ffffffff8211e96c>] tty_open+0x46c/0xe20 drivers/tty/tty_io.c:2125
1 lock held by init/11074:
 #0:  (tty_mutex){+.+.+.}, at: [<ffffffff8211e96c>] tty_open_by_driver drivers/tty/tty_io.c:2047 [inline]
 #0:  (tty_mutex){+.+.+.}, at: [<ffffffff8211e96c>] tty_open+0x46c/0xe20 drivers/tty/tty_io.c:2125

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

NMI backtrace for cpu 1
CPU: 1 PID: 519 Comm: khungtaskd Not tainted 4.9.122-g54068d6 #26
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d8527d08 ffffffff81eb8829 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810b9fa0 ffff8801d8527d40
 ffffffff81ec3b67 0000000000000001 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb8829>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb8829>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ec3b67>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ec3afa>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810ba0a4>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81368ff4>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81368ff4>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81368ff4>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81368ff4>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119f38d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff83a00e9c>] 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: 11073 Comm: init Not tainted 4.9.122-g54068d6 #26
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801b8fe9800 task.stack: ffff8801d4868000
RIP: 0010:[<ffffffff8215533b>] 
c [<ffffffff8215533b>] inb arch/x86/include/asm/io.h:316 [inline]
RIP: 0010:[<ffffffff8215533b>] 
c [<ffffffff8215533b>] io_serial_in+0x6b/0x90 drivers/tty/serial/8250/8250_port.c:414
RSP: 0000:ffff8801d486f520  EFLAGS: 00000002
RAX: dffffc0000000020 RBX: 00000000000003fd RCX: 0000000000000000
RDX: 00000000000003fd RSI: ffffffff821552e1 RDI: ffffffff864ace78
RBP: ffff8801d486f530 R08: ffff8801b8fea138 R09: 0000000000000001
R10: ffff8801b8fe9800 R11: 1ffff100371fd422 R12: ffffffff864ace40
R13: 0000000000000020 R14: fffffbfff0c95a0f R15: fffffbfff0c959d1
FS:  00007fa8a272f7a0(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f10298fda13 CR3: 00000001ca744000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff864ace40
c 0000000000002707
c ffff8801d486f580
c ffffffff82156f04
c
 ffff8801d486f5b8
c ffffffff864ace88
c ffffffff864ad07a
c ffffffff864ace40
c
 0000000000000030
c ffffffff82157050
c dffffc0000000000
c 0000000000000030
c
Call Trace:
 [<ffffffff82156f04>] serial_in drivers/tty/serial/8250/8250.h:111 [inline]
 [<ffffffff82156f04>] wait_for_xmitr+0x94/0x1e0 drivers/tty/serial/8250/8250_port.c:1998
 [<ffffffff8215706f>] serial8250_console_putchar+0x1f/0x60 drivers/tty/serial/8250/8250_port.c:3104
 [<ffffffff8213f899>] uart_console_write+0x59/0xf0 drivers/tty/serial/serial_core.c:1859
 [<ffffffff82163288>] serial8250_console_write+0x528/0x820 drivers/tty/serial/8250/8250_port.c:3170
 [<ffffffff8214fdef>] univ8250_console_write+0x5f/0x70 drivers/tty/serial/8250/8250_core.c:594
 [<ffffffff8125df4d>] call_console_drivers.isra.18.constprop.28+0x1ad/0x360 kernel/printk/printk.c:1589
 [<ffffffff81260d4f>] console_unlock+0x42f/0xb40 kernel/printk/printk.c:2449
 [<ffffffff81262197>] console_device+0x97/0xc0 kernel/printk/printk.c:2557
 [<ffffffff8211ec1a>] tty_lookup_driver drivers/tty/tty_io.c:2003 [inline]
 [<ffffffff8211ec1a>] tty_open_by_driver drivers/tty/tty_io.c:2048 [inline]
 [<ffffffff8211ec1a>] tty_open+0x71a/0xe20 drivers/tty/tty_io.c:2125
 [<ffffffff8158295d>] chrdev_open+0x22d/0x4c0 fs/char_dev.c:392
 [<ffffffff8156d843>] do_dentry_open+0x703/0xc80 fs/open.c:766
 [<ffffffff8157102c>] vfs_open+0x11c/0x210 fs/open.c:879
 [<ffffffff815a8168>] do_last fs/namei.c:3410 [inline]
 [<ffffffff815a8168>] path_openat+0x758/0x3590 fs/namei.c:3534
 [<ffffffff815af267>] do_filp_open+0x197/0x270 fs/namei.c:3568
 [<ffffffff81571a3d>] do_sys_open+0x30d/0x5c0 fs/open.c:1072
 [<ffffffff81571d1d>] SYSC_open fs/open.c:1090 [inline]
 [<ffffffff81571d1d>] SyS_open+0x2d/0x40 fs/open.c:1085
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff83a00cd3>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 
c24 
cc9 
c00 
c00 
c00 
c49 
c8d 
c7c 
c24 
c38 
c48 
cb8 
c00 
c00 
c00 
c00 
c00 
cfc 
cff 
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c48 
c89 
cfa 
c48 
cc1 
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c03 
cd3 
ce3 
c80 
c3c 
c02 
c00 
c75 
c17 
c41 
c03 
c5c 
c24 
c38 
c89 
cda 
cec 
c<5b> 
c0f 
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cc0 
c41 
c5c 
c5d 
cc3 
ce8 
c48 
c9f 
c3e 
cff 
ceb 
cc2 
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c3e 
cff 
ceb 
c