INFO: task syz-executor0:3868 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   D26232  3868      1 0x00000004
 ffff8801d940c800 ffff8801b7cc0540 ffff8801b7d739c0 ffff8801b7149800
 ffff8801db221c18 ffff8801a802fb40 ffffffff839efdcd 0000000000000002
 0000000041b58ab3 ffffffff843bbbe4 00ffffff81223830 ffff8801db2224e8
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 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-executor0/3868:
 #0:  (&type->s_umount_key#38){+.+...}, at: [<ffffffff8157e7d9>] deactivate_super+0x89/0xd0 fs/super.c:340

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

NMI backtrace for cpu 0
CPU: 0 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
 ffff8801d8637d08 ffffffff81eb8829 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b9fa0 ffff8801d8637d40
 ffffffff81ec3b67 0000000000000000 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 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 6 Comm: kworker/u4:0 Not tainted 4.9.122-g54068d6 #26
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:[<ffffffff81238c8a>] 
c [<ffffffff81238c8a>] validate_chain kernel/locking/lockdep.c:2235 [inline]
RIP: 0010:[<ffffffff81238c8a>] 
c [<ffffffff81238c8a>] __lock_acquire+0x85a/0x4070 kernel/locking/lockdep.c:3345
RSP: 0018:ffff8801d9a47400  EFLAGS: 00000046
RAX: dffffc0000000000 RBX: ffff8801d9a38940 RCX: 0000000072742dc7
RDX: 000000009430f3e9 RSI: ffff8801d9a38940 RDI: 0000000000000000
RBP: ffff8801d9a475b0 R08: ffff8801d9a38960 R09: 0000000000000000
R10: ffff8801d9a38000 R11: 1ffff1003b347127 R12: 0000000092c832a4
R13: 0000000000000000 R14: 00000000d1d422dd R15: 408256569430f3e9
FS:  0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f076c487000 CR3: 00000001ca269000 CR4: 00000000001606f0
Stack:
 0000000041b58ab3
c ffffffff843c40f8
c ffffffff81238430
c ffffffff843c40f8
c
 ffffffff81238430
c ffffffff83a00917
c ffff8801b7cc0000
c 0000000000000001
c
 ffff8801d9a38000
c ffff8801d9a47468
c ffffffff855b6f70
c ffff8801db321c00
c
Call Trace:
 [<ffffffff8123cf10>] lock_acquire+0x130/0x3e0 kernel/locking/lockdep.c:3756
 [<ffffffff83a00066>] __raw_spin_lock include/linux/spinlock_api_smp.h:144 [inline]
 [<ffffffff83a00066>] _raw_spin_lock+0x36/0x50 kernel/locking/spinlock.c:151
 [<ffffffff81627ab6>] spin_lock include/linux/spinlock.h:302 [inline]
 [<ffffffff81627ab6>] __find_get_block_slow+0xe6/0x330 fs/buffer.c:216
 [<ffffffff8162803e>] __find_get_block+0x23e/0x4c0 fs/buffer.c:1360
 [<ffffffff81628e49>] __getblk_slow fs/buffer.c:1101 [inline]
 [<ffffffff81628e49>] __getblk_gfp+0x189/0x710 fs/buffer.c:1386
 [<ffffffff8162c7ed>] __bread_gfp+0x2d/0x270 fs/buffer.c:1420
 [<ffffffff818da9b1>] sb_bread include/linux/buffer_head.h:300 [inline]
 [<ffffffff818da9b1>] fat_clusters_flush+0x111/0x380 fs/fat/misc.c:69
 [<ffffffff818d4912>] fat_write_inode+0xf2/0x170 fs/fat/inode.c:898
 [<ffffffff81605e3d>] write_inode fs/fs-writeback.c:1180 [inline]
 [<ffffffff81605e3d>] __writeback_single_inode+0x86d/0x1020 fs/fs-writeback.c:1379
 [<ffffffff8160713c>] writeback_sb_inodes+0x4ac/0xe70 fs/fs-writeback.c:1584
 [<ffffffff8160813f>] wb_writeback+0x2cf/0xbd0 fs/fs-writeback.c:1760
 [<ffffffff8161166e>] wb_do_writeback fs/fs-writeback.c:1894 [inline]
 [<ffffffff8161166e>] wb_workfn+0x20e/0xdb0 fs/fs-writeback.c:1930
 [<ffffffff8118f421>] process_one_work+0x7e1/0x1500 kernel/workqueue.c:2092
 [<ffffffff81190216>] worker_thread+0xd6/0x10a0 kernel/workqueue.c:2226
 [<ffffffff8119f38d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff83a00e9c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Code: 
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cff 
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c00 
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c48 
cb8 
c00 
c00 
c00 
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cdf 
c<48> 
c8b 
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c24 
c78 
c48 
cc1 
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c03 
c0f 
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c04 
c02 
c84 
cc0 
c74 
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c03 
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c8e 
c