INFO: task syz-executor0:3878 blocked for more than 120 seconds.
      Not tainted 4.9.102-gd054505 #31
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor0   D27336  3878      1 0x00000004
 ffff8801d8194800 0000000000000000 ffff8801b738c000 ffff8801c32f0000
 ffff8801db221c18 ffff8801b2c2fb40 ffffffff839e69ed 0000000000000002
 0000000041b58ab3 ffffffff843b980b 00ffffff81221330 ffff8801db2224e8
Call Trace:
 [<ffffffff839e7fef>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff816024e9>] wb_wait_for_completion+0x149/0x1b0 fs/fs-writeback.c:221
 [<ffffffff81602757>] __writeback_inodes_sb_nr+0x207/0x300 fs/fs-writeback.c:2310
 [<ffffffff816028a7>] writeback_inodes_sb_nr fs/fs-writeback.c:2327 [inline]
 [<ffffffff816028a7>] writeback_inodes_sb+0x27/0x30 fs/fs-writeback.c:2342
 [<ffffffff8161a463>] __sync_filesystem fs/sync.c:35 [inline]
 [<ffffffff8161a463>] sync_filesystem+0x93/0x240 fs/sync.c:63
 [<ffffffff81579115>] generic_shutdown_super+0x75/0x300 fs/super.c:423
 [<ffffffff81579a4f>] kill_block_super+0x9f/0x120 fs/super.c:1127
 [<ffffffff81579dc5>] deactivate_locked_super+0x75/0xd0 fs/super.c:310
 [<ffffffff8157a7d1>] deactivate_super+0x91/0xd0 fs/super.c:341
 [<ffffffff815dc8f2>] cleanup_mnt+0xb2/0x160 fs/namespace.c:1134
 [<ffffffff815dca26>] __cleanup_mnt+0x16/0x20 fs/namespace.c:1141
 [<ffffffff8119818c>] 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
 [<ffffffff839f78d3>] 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
2 locks held by getty/3778:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f5a92>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8211f1b2>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2133
1 lock held by syz-executor0/3878:
 #0:  (&type->s_umount_key#37){++++..}, at: [<ffffffff8157a7c9>] deactivate_super+0x89/0xd0 fs/super.c:340

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

NMI backtrace for cpu 0
CPU: 0 PID: 519 Comm: khungtaskd Not tainted 4.9.102-gd054505 #31
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d871fd08 ffffffff81eb3489 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b9590 ffff8801d871fd40
 ffffffff81ebe787 0000000000000000 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb3489>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb3489>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebe787>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebe71a>] 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
 [<ffffffff839f7a9c>] 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 4.9.102-gd054505 #31
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:[<ffffffff8123b545>] 
c [<ffffffff8123b545>] __lock_release kernel/locking/lockdep.c:3548 [inline]
RIP: 0010:[<ffffffff8123b545>] 
c [<ffffffff8123b545>] lock_release+0x2e5/0xb80 kernel/locking/lockdep.c:3775
RSP: 0018:ffff8801d9a47588  EFLAGS: 00000046
RAX: 0000000000000003 RBX: ffff8801b6801028 RCX: ffff8801d9a38000
RDX: 0000000000000000 RSI: ffff8801b6801028 RDI: ffff8801d9a38962
RBP: ffff8801d9a47630 R08: ffff8801d9a38960 R09: 0000000000000001
R10: 0000000000000000 R11: 1ffff1003b347127 R12: dffffc0000000000
R13: ffff8801d9a38940 R14: ffff8801d9a38918 R15: 0000000000000003
FS:  0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f0e4f3c0000 CR3: 000000000461e000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 0000000000000246
c ffff8801d9a38000
c 0000000000000000
c 0000000000000000
c
 0000000000000000
c ffff8801d9a47628
c 0000000000000246
c 0000000000000000
c
 ffffffff81623866
c ffff8801d9a388c0
c ffff8801d9a388c8
c 0000000000000246
c
Call Trace:
 [<ffffffff839f6f1a>] __raw_spin_unlock include/linux/spinlock_api_smp.h:152 [inline]
 [<ffffffff839f6f1a>] _raw_spin_unlock+0x1a/0x50 kernel/locking/spinlock.c:183
 [<ffffffff81623972>] spin_unlock include/linux/spinlock.h:347 [inline]
 [<ffffffff81623972>] __find_get_block_slow+0x1f2/0x330 fs/buffer.c:248
 [<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
 [<ffffffff818d5421>] sb_bread include/linux/buffer_head.h:300 [inline]
 [<ffffffff818d5421>] fat_clusters_flush+0x111/0x380 fs/fat/misc.c:69
 [<ffffffff818cf3b2>] fat_write_inode+0xf2/0x170 fs/fat/inode.c:890
 [<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
 [<ffffffff81603eef>] wb_writeback+0x2cf/0xbd0 fs/fs-writeback.c:1760
 [<ffffffff8160d41e>] wb_do_writeback fs/fs-writeback.c:1894 [inline]
 [<ffffffff8160d41e>] wb_workfn+0x20e/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
 [<ffffffff839f7a9c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Code: 
c22 
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c<66> 
c41 
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c20 
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cb8 
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cfc 
c