INFO: task syz-executor6:11746 blocked for more than 120 seconds.
      Not tainted 4.9.109-ge1815b3 #49
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor6   D29088 11746   9006 0x00000004
 ffff8801b517c800 0000000000000000 ffff8801bd8aaa00 ffffffff84629800
 ffff8801db221c18 ffff880196e1fb58 ffffffff839e8a8d 0000000000000002
 0000000041b58ab3 ffffffff843b9d9b 00ffffff81221500 ffff8801db2224e8
Call Trace:
 [<ffffffff839ea08f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff81602ad9>] wb_wait_for_completion+0x149/0x1b0 fs/fs-writeback.c:221
 [<ffffffff81608269>] sync_inodes_sb+0x1a9/0x8d0 fs/fs-writeback.c:2412
 [<ffffffff8161a393>] sync_inodes_one_sb+0x43/0x60 fs/sync.c:73
 [<ffffffff8157ccb0>] iterate_supers+0x130/0x260 fs/super.c:593
 [<ffffffff8161aca2>] sys_sync+0xa2/0x170 fs/sync.c:112
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f9993>] 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/3774:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f7b32>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8211fce2>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2133
1 lock held by syz-executor6/11746:
 #0:  (&type->s_umount_key#42){++++..}, at: [<ffffffff8157cc61>] iterate_supers+0xe1/0x260 fs/super.c:591

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

NMI backtrace for cpu 0
CPU: 0 PID: 519 Comm: khungtaskd Not tainted 4.9.109-ge1815b3 #49
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d89c7d08 ffffffff81eb3e29 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b9580 ffff8801d89c7d40
 ffffffff81ebf127 0000000000000000 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb3e29>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb3e29>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebf127>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebf0ba>] 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
 [<ffffffff839f9b5c>] 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: 22 Comm: kworker/u4:1 Not tainted 4.9.109-ge1815b3 #49
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn
c (flush-7:0)
c
task: ffff8801d9aeb000 task.stack: ffff8801d9bd8000
RIP: 0010:[<ffffffff8122fbd4>] 
c [<ffffffff8122fbd4>] match_held_lock+0x14/0x570 kernel/locking/lockdep.c:3404
RSP: 0018:ffff8801d9bdf490  EFLAGS: 00000002
RAX: dffffc0000000000 RBX: ffff8801d9aeb000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff846defa0 RDI: ffff8801d9aeb968
RBP: ffff8801d9bdf4a8 R08: ffff8801d9aeb988 R09: 0000000000000001
R10: ffff8801d9aeb000 R11: 1ffff1003b35d72c R12: ffffed003b35d718
R13: ffff8801d9aeb8c8 R14: ffffffff846defa0 R15: 0000000000000004
FS:  0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f11d702c000 CR3: 00000001bfeb7000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff8801d9aeb8c8
c ffffffff846defa0
c 0000000000000004
c ffff8801d9bdf4e8
c
 ffffffff812301d2
c ffff8801d9aeb8c0
c 0000000000000246
c ffff8801d9aeb000
c
 ffffffff846defa0
c 0000000000000000
c ffff8801cbfe4e48
c ffff8801d9bdf510
c
Call Trace:
 [<ffffffff812301d2>] __lock_is_held+0xa2/0xf0 kernel/locking/lockdep.c:3597
 [<ffffffff81230a04>] lock_is_held+0xb4/0x140 kernel/locking/lockdep.c:3794
 [<ffffffff8127c114>] rcu_read_lock_held+0xa4/0xc0 kernel/rcu/update.c:297
 [<ffffffff81438dfb>] radix_tree_deref_slot include/linux/radix-tree.h:199 [inline]
 [<ffffffff81438dfb>] find_get_entry+0x34b/0x540 mm/filemap.c:1097
 [<ffffffff81439f2b>] pagecache_get_page+0x4b/0x720 mm/filemap.c:1203
 [<ffffffff81623e32>] find_get_page_flags include/linux/pagemap.h:264 [inline]
 [<ffffffff81623e32>] __find_get_block_slow+0xc2/0x330 fs/buffer.c:212
 [<ffffffff816243de>] __find_get_block+0x23e/0x4c0 fs/buffer.c:1360
 [<ffffffff816251e9>] __getblk_slow fs/buffer.c:1101 [inline]
 [<ffffffff816251e9>] __getblk_gfp+0x189/0x710 fs/buffer.c:1386
 [<ffffffff81628b8d>] __bread_gfp+0x2d/0x270 fs/buffer.c:1420
 [<ffffffff818d5dd1>] sb_bread include/linux/buffer_head.h:300 [inline]
 [<ffffffff818d5dd1>] fat_clusters_flush+0x111/0x380 fs/fat/misc.c:69
 [<ffffffff818cfd62>] fat_write_inode+0xf2/0x170 fs/fat/inode.c:890
 [<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
 [<ffffffff839f9b5c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Code: 
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