b_state=0x0000002b, b_size=512
device loop0 blocksize: 4096
__find_get_block_slow() failed. block=1, b_blocknr=8
b_state=0x0000002b, b_size=512
device loop0 blocksize: 4096
INFO: task syz-executor0:3881 blocked for more than 140 seconds.
      Not tainted 4.9.113-g47bbcd6 #10
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor0   D26952  3881      1 0x00000004
 ffff8801d8e01800 0000000000000000 ffff8801ccd86a00 ffff8801d99b3000
 ffff8801db221c18 ffff8801a0647b40 ffffffff839e909d 0000000000000002
 0000000041b58ab3 ffffffff843bbae3 00ffffff81221550 ffff8801db2224e8
Call Trace:
 [<ffffffff839ea69f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3553
 [<ffffffff81602c89>] wb_wait_for_completion+0x149/0x1b0 fs/fs-writeback.c:221
 [<ffffffff81602ef7>] __writeback_inodes_sb_nr+0x207/0x300 fs/fs-writeback.c:2310
 [<ffffffff81603047>] writeback_inodes_sb_nr fs/fs-writeback.c:2327 [inline]
 [<ffffffff81603047>] writeback_inodes_sb+0x27/0x30 fs/fs-writeback.c:2342
 [<ffffffff8161ac03>] __sync_filesystem fs/sync.c:35 [inline]
 [<ffffffff8161ac03>] sync_filesystem+0x93/0x240 fs/sync.c:63
 [<ffffffff81579635>] generic_shutdown_super+0x75/0x300 fs/super.c:423
 [<ffffffff81579f6f>] kill_block_super+0x9f/0x120 fs/super.c:1127
 [<ffffffff8157a2e5>] deactivate_locked_super+0x75/0xd0 fs/super.c:310
 [<ffffffff8157acf1>] deactivate_super+0x91/0xd0 fs/super.c:341
 [<ffffffff815dd092>] cleanup_mnt+0xb2/0x160 fs/namespace.c:1134
 [<ffffffff815dd1c6>] __cleanup_mnt+0x16/0x20 fs/namespace.c:1141
 [<ffffffff8119838c>] 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
 [<ffffffff839f9f93>] 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: [<ffffffff8136675c>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136675c>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81425de7>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
1 lock held by rsyslogd/3681:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<ffffffff815d81ec>] __fdget_pos+0xac/0xd0 fs/file.c:781
2 locks held by getty/3777:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f8142>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8211ee22>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2142
1 lock held by syz-executor0/3881:
 #0:  (&type->s_umount_key#38){+.+...}, at: [<ffffffff8157ace9>] deactivate_super+0x89/0xd0 fs/super.c:340
1 lock held by syz-executor3/12100:
 #0:  (acct_on_mutex){+.+.+.}, at: [<ffffffff812f3ac3>] SYSC_acct kernel/acct.c:282 [inline]
 #0:  (acct_on_mutex){+.+.+.}, at: [<ffffffff812f3ac3>] SyS_acct+0x83/0x840 kernel/acct.c:270
1 lock held by syz-executor3/12101:
 #0:  (acct_on_mutex){+.+.+.}, at: [<ffffffff812f3ac3>] SYSC_acct kernel/acct.c:282 [inline]
 #0:  (acct_on_mutex){+.+.+.}, at: [<ffffffff812f3ac3>] SyS_acct+0x83/0x840 kernel/acct.c:270
1 lock held by init/12105:
 #0:  (tty_mutex){+.+.+.}, at: [<ffffffff8211922c>] tty_open_by_driver drivers/tty/tty_io.c:2047 [inline]
 #0:  (tty_mutex){+.+.+.}, at: [<ffffffff8211922c>] tty_open+0x46c/0xe20 drivers/tty/tty_io.c:2125
1 lock held by init/12106:
 #0:  (tty_mutex){+.+.+.}, at: [<ffffffff8211922c>] tty_open_by_driver drivers/tty/tty_io.c:2047 [inline]
 #0:  (tty_mutex){+.+.+.}, at: [<ffffffff8211922c>] tty_open+0x46c/0xe20 drivers/tty/tty_io.c:2125
1 lock held by init/12107:
 #0:  (tty_mutex){+.+.+.}, at: [<ffffffff8211922c>] tty_open_by_driver drivers/tty/tty_io.c:2047 [inline]
 #0:  (tty_mutex){+.+.+.}, at: [<ffffffff8211922c>] tty_open+0x46c/0xe20 drivers/tty/tty_io.c:2125
1 lock held by init/12108:
 #0:  (tty_mutex){+.+.+.}, at: [<ffffffff8211922c>] tty_open_by_driver drivers/tty/tty_io.c:2047 [inline]
 #0:  (tty_mutex){+.+.+.}, at: [<ffffffff8211922c>] tty_open+0x46c/0xe20 drivers/tty/tty_io.c:2125
1 lock held by init/12109:
 #0:  (tty_mutex){+.+.+.}, at: [<ffffffff8211922c>] tty_open_by_driver drivers/tty/tty_io.c:2047 [inline]
 #0:  (tty_mutex){+.+.+.}, at: [<ffffffff8211922c>] tty_open+0x46c/0xe20 drivers/tty/tty_io.c:2125
1 lock held by init/12110:
 #0:  (tty_mutex){+.+.+.}, at: [<ffffffff8211922c>] tty_open_by_driver drivers/tty/tty_io.c:2047 [inline]
 #0:  (tty_mutex){+.+.+.}, at: [<ffffffff8211922c>] tty_open+0x46c/0xe20 drivers/tty/tty_io.c:2125

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

NMI backtrace for cpu 0
CPU: 0 PID: 519 Comm: khungtaskd Not tainted 4.9.113-g47bbcd6 #10
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d85ffd08 ffffffff81eb32a9 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b9bd0 ffff8801d85ffd40
 ffffffff81ebe5a7 0000000000000000 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb32a9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb32a9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebe5a7>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebe53a>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b9cd4>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81366cf4>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81366cf4>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81366cf4>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81366cf4>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119d0ad>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839fa15c>] 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: 12046 Comm: syz-executor3 Not tainted 4.9.113-g47bbcd6 #10
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff88019a259800 task.stack: ffff8801c9930000
RIP: 0010:[<ffffffff8214fb5b>] 
c [<ffffffff8214fb5b>] inb arch/x86/include/asm/io.h:316 [inline]
RIP: 0010:[<ffffffff8214fb5b>] 
c [<ffffffff8214fb5b>] io_serial_in+0x6b/0x90 drivers/tty/serial/8250/8250_port.c:414
RSP: 0018:ffff8801c9937690  EFLAGS: 00000002
RAX: dffffc0000000000 RBX: 00000000000003fd RCX: 0000000000000000
RDX: 00000000000003fd RSI: ffffffff8214fb01 RDI: ffffffff864aae78
RBP: ffff8801c99376a0 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffffffff864aae40
R13: 0000000000000020 R14: fffffbfff0c9560f R15: fffffbfff0c955d1
FS:  00007f0818ed6700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000001eb5b10 CR3: 00000001c98e6000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff864aae40
c 0000000000002707
c ffff8801c99376f0
c ffffffff82151724
c
 ffffffff81ede598
c ffffffff864aae88
c ffffffff864ab07a
c ffffffff864aae40
c
 0000000000000020
c ffffffff82151870
c dffffc0000000000
c 0000000000000020
c
Call Trace:
 [<ffffffff82151724>] serial_in drivers/tty/serial/8250/8250.h:111 [inline]
 [<ffffffff82151724>] wait_for_xmitr+0x94/0x1e0 drivers/tty/serial/8250/8250_port.c:1998
 [<ffffffff8215188f>] serial8250_console_putchar+0x1f/0x60 drivers/tty/serial/8250/8250_port.c:3104
 [<ffffffff8213a0b9>] uart_console_write+0x59/0xf0 drivers/tty/serial/serial_core.c:1859
 [<ffffffff8215daa8>] serial8250_console_write+0x528/0x820 drivers/tty/serial/8250/8250_port.c:3170
 [<ffffffff8214a60f>] univ8250_console_write+0x5f/0x70 drivers/tty/serial/8250/8250_core.c:594
 [<ffffffff8125bccd>] call_console_drivers.isra.18.constprop.28+0x1ad/0x360 kernel/printk/printk.c:1589
 [<ffffffff8125eacf>] console_unlock+0x42f/0xb40 kernel/printk/printk.c:2449
 [<ffffffff8125f628>] vprintk_emit+0x448/0x790 kernel/printk/printk.c:1903
 [<ffffffff8125f998>] vprintk+0x28/0x30 kernel/printk/printk.c:1913
 [<ffffffff8125f9bd>] vprintk_default+0x1d/0x30 kernel/printk/printk.c:1914
 [<ffffffff8142cbbc>] vprintk_func kernel/printk/internal.h:36 [inline]
 [<ffffffff8142cbbc>] printk+0xaf/0xd7 kernel/printk/printk.c:1975
 [<ffffffff8143133a>] check_free_space.cold.4+0x67/0xb0 kernel/acct.c:121
 [<ffffffff812f29e7>] do_acct_process+0x1b7/0x1130 kernel/acct.c:487
 [<ffffffff812f398c>] acct_pin_kill+0x2c/0xe0 kernel/acct.c:171
 [<ffffffff8161efc7>] pin_kill+0x167/0x630 fs/fs_pin.c:49
 [<ffffffff812f3fa0>] acct_on kernel/acct.c:251 [inline]
 [<ffffffff812f3fa0>] SYSC_acct kernel/acct.c:283 [inline]
 [<ffffffff812f3fa0>] SyS_acct+0x560/0x840 kernel/acct.c:270
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f9f93>] 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 
cdf 
c48 
c89 
cfa 
c48 
cc1 
cea 
c03 
cd3 
ce3 
c80 
c3c 
c02 
c00 
c75 
c17 
c41 
c03 
c5c 
c24 
c38 
c89 
cda 
cec 
c<5b> 
c0f 
cb6 
cc0 
c41 
c5c 
c5d 
cc3 
ce8 
c58 
cc0 
c3e 
cff 
ceb 
cc2 
ce8 
cb1 
cc0 
c3e 
cff 
ceb 
c