device loop0 blocksize: 4096
__find_get_block_slow() failed. block=3, b_blocknr=24
b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
__find_get_block_slow() failed. block=1, b_blocknr=8
INFO: task syz-executor0:29964 blocked for more than 120 seconds.
      Not tainted 4.9.103-g0cecdf8 #35
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor0   D30840 29964  13351 0x00000004
 ffff88018c376000 ffff8801be426f40 ffff8801867db9c0 ffff88018791c800
 ffff8801db221c18 ffff88018cbcfce8 ffffffff839e711d ffff88018c3768c8
 ffffed003186ed18 ffff88018c376000 00fffc0000000000 ffff8801db2224e8
Call Trace:
 [<ffffffff839e871f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839e90a3>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3590
 [<ffffffff839ed526>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff839ed526>] mutex_lock_nested+0x326/0x870 kernel/locking/mutex.c:621
 [<ffffffff815d7a4c>] __fdget_pos+0xac/0xd0 fs/file.c:781
 [<ffffffff8157635e>] fdget_pos include/linux/file.h:66 [inline]
 [<ffffffff8157635e>] SYSC_write fs/read_write.c:599 [inline]
 [<ffffffff8157635e>] SyS_write+0x7e/0x1c0 fs/read_write.c:596
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f8013>] 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: [<ffffffff8136688c>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136688c>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81425e10>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
1 lock held by rsyslogd/3630:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<ffffffff815d7a4c>] __fdget_pos+0xac/0xd0 fs/file.c:781
2 locks held by getty/3726:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f61c2>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8211f1d2>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2133
1 lock held by syz-executor0/29964:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<ffffffff815d7a4c>] __fdget_pos+0xac/0xd0 fs/file.c:781
2 locks held by syz-executor0/29967:
 #0:  (sb_writers#14){.+.+.+}, at: [<ffffffff815e02ef>] sb_start_write include/linux/fs.h:1573 [inline]
 #0:  (sb_writers#14){.+.+.+}, at: [<ffffffff815e02ef>] mnt_want_write+0x3f/0xb0 fs/namespace.c:391
 #1:  (&sb->s_type->i_mutex_key#18){++++++}, at: [<ffffffff8156a318>] inode_lock include/linux/fs.h:766 [inline]
 #1:  (&sb->s_type->i_mutex_key#18){++++++}, at: [<ffffffff8156a318>] do_truncate2+0x128/0x1f0 fs/open.c:61

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

NMI backtrace for cpu 1
CPU: 1 PID: 519 Comm: khungtaskd Not tainted 4.9.103-g0cecdf8 #35
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d86b7d08 ffffffff81eb34a9 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810b9590 ffff8801d86b7d40
 ffffffff81ebe7a7 0000000000000001 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb34a9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb34a9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebe7a7>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebe73a>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b9694>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81366e24>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81366e24>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81366e24>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81366e24>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119cead>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f81dc>] 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: 397 Comm: kworker/u4:2 Not tainted 4.9.103-g0cecdf8 #35
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn
c (flush-7:0)
c
task: ffff8801d8a01800 task.stack: ffff8801d8ad8000
RIP: 0010:[<ffffffff8214fb2b>] 
c [<ffffffff8214fb2b>] inb arch/x86/include/asm/io.h:316 [inline]
RIP: 0010:[<ffffffff8214fb2b>] 
c [<ffffffff8214fb2b>] io_serial_in+0x6b/0x90 drivers/tty/serial/8250/8250_port.c:414
RSP: 0018:ffff8801d8adf0a8  EFLAGS: 00000002
RAX: dffffc0000000000 RBX: 00000000000003fd RCX: 0000000000000000
RDX: 00000000000003fd RSI: ffffffff8214fad1 RDI: ffffffff864aae78
RBP: ffff8801d8adf0b8 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffffffff864aae40
R13: 0000000000000020 R14: fffffbfff0c9560f R15: fffffbfff0c955d1
FS:  0000000000000000(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f3f3ca543c0 CR3: 00000001cb758000 CR4: 00000000001606f0
DR0: 00000000200001c0 DR1: 00000000200001c0 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
Stack:
 ffffffff864aae40
c 0000000000002710
c ffff8801d8adf108
c ffffffff821516f4
c
 ffffffff81ede798
c ffffffff864aae88
c ffffffff864ab07a
c ffffffff864aae40
c
 0000000000000037
c ffffffff82151840
c dffffc0000000000
c 0000000000000037
c
Call Trace:
 [<ffffffff821516f4>] serial_in drivers/tty/serial/8250/8250.h:111 [inline]
 [<ffffffff821516f4>] wait_for_xmitr+0x94/0x1e0 drivers/tty/serial/8250/8250_port.c:1998
 [<ffffffff8215185f>] serial8250_console_putchar+0x1f/0x60 drivers/tty/serial/8250/8250_port.c:3104
 [<ffffffff8213a089>] uart_console_write+0x59/0xf0 drivers/tty/serial/serial_core.c:1859
 [<ffffffff8215da78>] serial8250_console_write+0x528/0x820 drivers/tty/serial/8250/8250_port.c:3170
 [<ffffffff8214a5df>] univ8250_console_write+0x5f/0x70 drivers/tty/serial/8250/8250_core.c:594
 [<ffffffff8125bfcd>] call_console_drivers.isra.18.constprop.28+0x1ad/0x360 kernel/printk/printk.c:1589
 [<ffffffff8125edcf>] console_unlock+0x42f/0xb40 kernel/printk/printk.c:2449
 [<ffffffff8125f928>] vprintk_emit+0x448/0x790 kernel/printk/printk.c:1903
 [<ffffffff8125fc98>] vprintk+0x28/0x30 kernel/printk/printk.c:1913
 [<ffffffff8125fcbd>] vprintk_default+0x1d/0x30 kernel/printk/printk.c:1914
 [<ffffffff8142cbe5>] vprintk_func kernel/printk/internal.h:36 [inline]
 [<ffffffff8142cbe5>] printk+0xaf/0xd7 kernel/printk/printk.c:1975
 [<ffffffff81cb9a2a>] __find_get_block_slow.cold.57+0x37/0xf0 fs/buffer.c:238
 [<ffffffff81623dee>] __find_get_block+0x23e/0x4c0 fs/buffer.c:1360
 [<ffffffff81624bf9>] __getblk_slow fs/buffer.c:1101 [inline]
 [<ffffffff81624bf9>] __getblk_gfp+0x189/0x710 fs/buffer.c:1386
 [<ffffffff8162859d>] __bread_gfp+0x2d/0x270 fs/buffer.c:1420
 [<ffffffff818cb14b>] sb_bread include/linux/buffer_head.h:300 [inline]
 [<ffffffff818cb14b>] __fat_write_inode+0x2ab/0x980 fs/fat/inode.c:844
 [<ffffffff818cf359>] fat_write_inode+0x79/0x170 fs/fat/inode.c:893
 [<ffffffff81601bed>] write_inode fs/fs-writeback.c:1180 [inline]
 [<ffffffff81601bed>] __writeback_single_inode+0x86d/0x1020 fs/fs-writeback.c:1379
 [<ffffffff81602eec>] writeback_sb_inodes+0x4ac/0xe70 fs/fs-writeback.c:1584
 [<ffffffff816039ab>] __writeback_inodes_wb+0xfb/0x1e0 fs/fs-writeback.c:1653
 [<ffffffff81604132>] wb_writeback+0x512/0xbd0 fs/fs-writeback.c:1762
 [<ffffffff8160da60>] wb_check_old_data_flush fs/fs-writeback.c:1877 [inline]
 [<ffffffff8160da60>] wb_do_writeback fs/fs-writeback.c:1901 [inline]
 [<ffffffff8160da60>] wb_workfn+0x850/0xdb0 fs/fs-writeback.c:1930
 [<ffffffff8118cf81>] process_one_work+0x7e1/0x1500 kernel/workqueue.c:2092
 [<ffffffff8118dd76>] worker_thread+0xd6/0x10a0 kernel/workqueue.c:2226
 [<ffffffff8119cead>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f81dc>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Code: 
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c