__find_get_block_slow() failed. block=1, b_blocknr=8
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
INFO: task syz-executor0:3879 blocked for more than 140 seconds.
      Not tainted 4.9.119-g92e8704 #22
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor0   D26872  3879      1 0x00000004
 ffff8801cb350000 ffff8801bd864a80 ffff8801b7ad7480 ffff8801d86a8000
 ffff8801db221c18 ffff8801a51c7b40 ffffffff839ebdcd 0000000000000002
 0000000041b58ab3 ffffffff843bc37b 00ffffff81221590 ffff8801db2224e8
Call Trace:
 [<ffffffff839ed3cf>] schedule+0x7f/0x1b0 kernel/sched/core.c:3553
 [<ffffffff81603039>] wb_wait_for_completion+0x149/0x1b0 fs/fs-writeback.c:221
 [<ffffffff816032a7>] __writeback_inodes_sb_nr+0x207/0x300 fs/fs-writeback.c:2310
 [<ffffffff816033f7>] writeback_inodes_sb_nr fs/fs-writeback.c:2327 [inline]
 [<ffffffff816033f7>] writeback_inodes_sb+0x27/0x30 fs/fs-writeback.c:2342
 [<ffffffff8161afb3>] __sync_filesystem fs/sync.c:35 [inline]
 [<ffffffff8161afb3>] sync_filesystem+0x93/0x240 fs/sync.c:63
 [<ffffffff815799e5>] generic_shutdown_super+0x75/0x300 fs/super.c:423
 [<ffffffff8157a31f>] kill_block_super+0x9f/0x120 fs/super.c:1127
 [<ffffffff8157a695>] deactivate_locked_super+0x75/0xd0 fs/super.c:310
 [<ffffffff8157b0a1>] deactivate_super+0x91/0xd0 fs/super.c:341
 [<ffffffff815dd442>] cleanup_mnt+0xb2/0x160 fs/namespace.c:1134
 [<ffffffff815dd576>] __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
 [<ffffffff839fccd3>] 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: [<ffffffff813667bc>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff813667bc>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81426027>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
1 lock held by rsyslogd/3682:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<ffffffff815d859c>] __fdget_pos+0xac/0xd0 fs/file.c:781
2 locks held by getty/3778:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839fae72>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff821208d2>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2142
1 lock held by syz-executor0/3879:
 #0:  (&type->s_umount_key#39){+.+...}, at: [<ffffffff8157b099>] deactivate_super+0x89/0xd0 fs/super.c:340

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

NMI backtrace for cpu 0
CPU: 0 PID: 519 Comm: khungtaskd Not tainted 4.9.119-g92e8704 #22
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d840fd08 ffffffff81eb4be9 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b9bd0 ffff8801d840fd40
 ffffffff81ebfee7 0000000000000000 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb4be9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb4be9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebfee7>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebfe7a>] 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
 [<ffffffff81366d54>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81366d54>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81366d54>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81366d54>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119d0ed>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839fce9c>] 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: 6 Comm: kworker/u4:0 Not tainted 4.9.119-g92e8704 #22
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn
c (flush-7:0)
c
task: ffff8801d9a38000 task.stack: ffff8801d9a40000
RIP: 0010:[<ffffffff81f1c62b>] 
c [<ffffffff81f1c62b>] check_preemption_disabled+0x3b/0x170 lib/smp_processor_id.c:51
RSP: 0018:ffff8801d9a470a0  EFLAGS: 00000093
RAX: ffff8801d9a38000 RBX: 0000000000000001 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff81f1c62b RDI: ffffffff83e2e3e0
RBP: ffff8801d9a470d0 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffffffff83e2e3e0
R13: ffffffff83e2e3a0 R14: 0000000000000001 R15: fffffbfff0c955d9
FS:  0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000017e7000 CR3: 00000001ca138000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 0000000041b58ab3
c 0000009a717afcaa
c 0000009a717afa72
c 00000000000008fd
c
 0000000000000001
c fffffbfff0c955d9
c ffff8801d9a470e0
c ffffffff81f1c77c
c
 ffff8801d9a47110
c ffffffff81ee3d62
c ffffffff864aae80
c 000000000000270a
c
Call Trace:
 [<ffffffff81f1c77c>] debug_smp_processor_id+0x1c/0x20 lib/smp_processor_id.c:56
 [<ffffffff81ee3d62>] delay_tsc+0x42/0xc0 arch/x86/lib/delay.c:78
 [<ffffffff81ee3c91>] __delay arch/x86/lib/delay.c:160 [inline]
 [<ffffffff81ee3c91>] __const_udelay+0x31/0x40 arch/x86/lib/delay.c:174
 [<ffffffff8215324f>] wait_for_xmitr+0x6f/0x1e0 drivers/tty/serial/8250/8250_port.c:2006
 [<ffffffff821533df>] serial8250_console_putchar+0x1f/0x60 drivers/tty/serial/8250/8250_port.c:3104
 [<ffffffff8213bc09>] uart_console_write+0x59/0xf0 drivers/tty/serial/serial_core.c:1859
 [<ffffffff8215f5f8>] serial8250_console_write+0x528/0x820 drivers/tty/serial/8250/8250_port.c:3170
 [<ffffffff8214c15f>] univ8250_console_write+0x5f/0x70 drivers/tty/serial/8250/8250_core.c:594
 [<ffffffff8125bcad>] call_console_drivers.isra.18.constprop.28+0x1ad/0x360 kernel/printk/printk.c:1589
 [<ffffffff8125eaaf>] console_unlock+0x42f/0xb40 kernel/printk/printk.c:2449
 [<ffffffff8125f608>] vprintk_emit+0x448/0x790 kernel/printk/printk.c:1903
 [<ffffffff8125f978>] vprintk+0x28/0x30 kernel/printk/printk.c:1913
 [<ffffffff8125f99d>] vprintk_default+0x1d/0x30 kernel/printk/printk.c:1914
 [<ffffffff8142cdfc>] vprintk_func kernel/printk/internal.h:36 [inline]
 [<ffffffff8142cdfc>] printk+0xaf/0xd7 kernel/printk/printk.c:1975
 [<ffffffff81cbac45>] __find_get_block_slow.cold.57+0x82/0xf0 fs/buffer.c:242
 [<ffffffff8162493e>] __find_get_block+0x23e/0x4c0 fs/buffer.c:1360
 [<ffffffff81625749>] __getblk_slow fs/buffer.c:1101 [inline]
 [<ffffffff81625749>] __getblk_gfp+0x189/0x710 fs/buffer.c:1386
 [<ffffffff816290ed>] __bread_gfp+0x2d/0x270 fs/buffer.c:1420
 [<ffffffff818cc60b>] sb_bread include/linux/buffer_head.h:300 [inline]
 [<ffffffff818cc60b>] __fat_write_inode+0x2ab/0x980 fs/fat/inode.c:852
 [<ffffffff818d08c9>] fat_write_inode+0x79/0x170 fs/fat/inode.c:901
 [<ffffffff8160273d>] write_inode fs/fs-writeback.c:1180 [inline]
 [<ffffffff8160273d>] __writeback_single_inode+0x86d/0x1020 fs/fs-writeback.c:1379
 [<ffffffff81603a3c>] writeback_sb_inodes+0x4ac/0xe70 fs/fs-writeback.c:1584
 [<ffffffff81604a3f>] wb_writeback+0x2cf/0xbd0 fs/fs-writeback.c:1760
 [<ffffffff8160df6e>] wb_do_writeback fs/fs-writeback.c:1894 [inline]
 [<ffffffff8160df6e>] wb_workfn+0x20e/0xdb0 fs/fs-writeback.c:1930
 [<ffffffff8118d181>] process_one_work+0x7e1/0x1500 kernel/workqueue.c:2092
 [<ffffffff8118df76>] worker_thread+0xd6/0x10a0 kernel/workqueue.c:2226
 [<ffffffff8119d0ed>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839fce9c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Code: 
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