INFO: task syz-executor0:3771 blocked for more than 120 seconds.
      Not tainted 4.9.110-g00a0bcb #4
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor0   D27320  3771      1 0x00000004
 ffff8801c10f3000 0000000000000000 ffff8801da366f40 ffff8801ae640000
 ffff8801db221c18 ffff8801ae027b88 ffffffff839e6ded ffffffff812355f7
 0000000000000000 ffff8801c10f38c0 0000000600000007 ffff8801db2224e8
Call Trace:
 [<ffffffff839e83ef>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839f3a28>] __rwsem_down_write_failed_common kernel/locking/rwsem-xadd.c:526 [inline]
 [<ffffffff839f3a28>] rwsem_down_write_failed+0x598/0x990 kernel/locking/rwsem-xadd.c:555
 [<ffffffff81ee6607>] call_rwsem_down_write_failed+0x17/0x30 arch/x86/lib/rwsem.S:105
 [<ffffffff839f17fc>] __down_write arch/x86/include/asm/rwsem.h:125 [inline]
 [<ffffffff839f17fc>] down_write+0x5c/0xa0 kernel/locking/rwsem.c:54
 [<ffffffff8157ab99>] deactivate_super+0x89/0xd0 fs/super.c:340
 [<ffffffff815dcee2>] cleanup_mnt+0xb2/0x160 fs/namespace.c:1134
 [<ffffffff815dd016>] __cleanup_mnt+0x16/0x20 fs/namespace.c:1141
 [<ffffffff8119832c>] 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
 [<ffffffff839f7cd3>] 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: [<ffffffff8136662c>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136662c>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81425cb7>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3681:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f5e92>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff8211e1e2>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2133
1 lock held by syz-executor0/3771:
 #0:  (&type->s_umount_key#39){++++..}, at: [<ffffffff8157ab99>] deactivate_super+0x89/0xd0 fs/super.c:340
1 lock held by syz-executor6/9659:
 #0:  (&type->s_umount_key#39){++++..}, at: [<ffffffff8157cc61>] iterate_supers+0xe1/0x260 fs/super.c:591
1 lock held by syz-executor6/9690:
 #0:  (&type->s_umount_key#39){++++..}, at: [<ffffffff8157cc61>] iterate_supers+0xe1/0x260 fs/super.c:591

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

NMI backtrace for cpu 1
CPU: 1 PID: 519 Comm: khungtaskd Not tainted 4.9.110-g00a0bcb #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d905fd08 ffffffff81eb2329 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810b9580 ffff8801d905fd40
 ffffffff81ebd627 0000000000000001 0000000000000000 0000000000000002
Call Trace:
 [<ffffffff81eb2329>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb2329>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebd627>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebd5ba>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b9684>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81366bc4>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81366bc4>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81366bc4>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81366bc4>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119d04d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f7e9c>] 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: 6039 Comm: kworker/u4:2 Not tainted 4.9.110-g00a0bcb #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn
c (flush-7:0)
c
task: ffff8801ae640000 task.stack: ffff8801a00e8000
RIP: 0010:[<ffffffff81230a4f>] 
c [<ffffffff81230a4f>] arch_local_irq_restore arch/x86/include/asm/paravirt.h:768 [inline]
RIP: 0010:[<ffffffff81230a4f>] 
c [<ffffffff81230a4f>] lock_is_held+0xff/0x140 kernel/locking/lockdep.c:3796
RSP: 0018:ffff8801a00ef4e8  EFLAGS: 00000246
RAX: 0000000000000007 RBX: 0000000000000246 RCX: ffff8801ae640000
RDX: 0000000000000000 RSI: ffffffff846def60 RDI: 0000000000000246
RBP: ffff8801a00ef500 R08: ffff8801ae640960 R09: 0000000000000001
R10: 0000000000000000 R11: 1ffff10035cc8127 R12: ffff8801ae640000
R13: 0000000000000000 R14: 00000000000001c4 R15: ffff8801d9c14e48
FS:  0000000000000000(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ff190625000 CR3: 00000001c2c5d000 CR4: 00000000001606f0
DR0: 00000000200001c0 DR1: 00000000200001c0 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
Stack:
 ffff8801ae640000
c 0000000000000000
c ffffffff83ca4760
c ffff8801a00ef538
c
 ffffffff811bb52f
c ffff8801ae640000
c ffffffff83ca4760
c 00000000000001c4
c
 0000000000000000
c ffff8801d9c14e48
c ffff8801a00ef578
c ffffffff811bb625
c
Call Trace:
 [<ffffffff811bb52f>] ___might_sleep+0x1ff/0x260 kernel/sched/core.c:7958
 [<ffffffff811bb625>] __might_sleep+0x95/0x1a0 kernel/sched/core.c:7949
 [<ffffffff8143a29d>] lock_page include/linux/pagemap.h:452 [inline]
 [<ffffffff8143a29d>] pagecache_get_page+0x3bd/0x720 mm/filemap.c:1216
 [<ffffffff816252a9>] find_or_create_page include/linux/pagemap.h:309 [inline]
 [<ffffffff816252a9>] grow_dev_page fs/buffer.c:1005 [inline]
 [<ffffffff816252a9>] grow_buffers fs/buffer.c:1078 [inline]
 [<ffffffff816252a9>] __getblk_slow fs/buffer.c:1105 [inline]
 [<ffffffff816252a9>] __getblk_gfp+0x249/0x710 fs/buffer.c:1386
 [<ffffffff81628b8d>] __bread_gfp+0x2d/0x270 fs/buffer.c:1420
 [<ffffffff818cbb0b>] sb_bread include/linux/buffer_head.h:300 [inline]
 [<ffffffff818cbb0b>] __fat_write_inode+0x2ab/0x980 fs/fat/inode.c:844
 [<ffffffff818cfd19>] fat_write_inode+0x79/0x170 fs/fat/inode.c:893
 [<ffffffff816021dd>] write_inode fs/fs-writeback.c:1180 [inline]
 [<ffffffff816021dd>] __writeback_single_inode+0x86d/0x1020 fs/fs-writeback.c:1379
 [<ffffffff816034dc>] writeback_sb_inodes+0x4ac/0xe70 fs/fs-writeback.c:1584
 [<ffffffff81603f9b>] __writeback_inodes_wb+0xfb/0x1e0 fs/fs-writeback.c:1653
 [<ffffffff81604722>] wb_writeback+0x512/0xbd0 fs/fs-writeback.c:1762
 [<ffffffff8160da0e>] wb_do_writeback fs/fs-writeback.c:1894 [inline]
 [<ffffffff8160da0e>] wb_workfn+0x20e/0xdb0 fs/fs-writeback.c:1930
 [<ffffffff8118d121>] process_one_work+0x7e1/0x1500 kernel/workqueue.c:2092
 [<ffffffff8118df16>] worker_thread+0xd6/0x10a0 kernel/workqueue.c:2226
 [<ffffffff8119d04d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f7e9c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Code: 
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c<0f> 
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c