INFO: task syz-executor0:16654 blocked for more than 120 seconds.
      Not tainted 4.9.107-gdb2c520 #46
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor0   D30176 16654  15872 0x00000004
 ffff8801d7bb0000 0000000000000000 ffff8801c3ca0540 ffffffff84629800
 ffff8801db221c18 ffff880180abfce8 ffffffff839e8c1d ffff8801d7bb08c8
 ffffed003af76118 ffff8801d7bb0000 00fffc0000000000 ffff8801db2224e8
Call Trace:
 [<ffffffff839ea21f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839eaba3>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3590
 [<ffffffff839ef026>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff839ef026>] mutex_lock_nested+0x326/0x870 kernel/locking/mutex.c:621
 [<ffffffff815d7fac>] __fdget_pos+0xac/0xd0 fs/file.c:781
 [<ffffffff8157669e>] fdget_pos include/linux/file.h:66 [inline]
 [<ffffffff8157669e>] SYSC_write fs/read_write.c:599 [inline]
 [<ffffffff8157669e>] SyS_write+0x7e/0x1c0 fs/read_write.c:596
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f9b13>] 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/3637:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f7cc2>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8211fc62>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2133
1 lock held by syz-executor0/16654:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<ffffffff815d7fac>] __fdget_pos+0xac/0xd0 fs/file.c:781
1 lock held by syz-executor0/16657:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<ffffffff815d7fac>] __fdget_pos+0xac/0xd0 fs/file.c:781

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

NMI backtrace for cpu 0
CPU: 0 PID: 519 Comm: khungtaskd Not tainted 4.9.107-gdb2c520 #46
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d86afd08 ffffffff81eb3da9 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b96a0 ffff8801d86afd40
 ffffffff81ebf0a7 0000000000000000 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb3da9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb3da9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebf0a7>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebf03a>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b97a4>] 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
 [<ffffffff839f9cdc>] 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: 16598 Comm: syz-executor0 Not tainted 4.9.107-gdb2c520 #46
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801cdcb1800 task.stack: ffff880182f80000
RIP: 0010:[<ffffffff81235597>] 
c [<ffffffff81235597>] mark_held_locks+0x67/0x130 kernel/locking/lockdep.c:2652
RSP: 0018:ffff880182f87090  EFLAGS: 00000046
RAX: 0000000000000004 RBX: 0000000000000000 RCX: 1ffff10039b9642c
RDX: 1ffff10039b96418 RSI: 0000000000000001 RDI: ffff8801cdcb1800
RBP: ffff880182f870d0 R08: ffff8801cdcb2160 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000004
R13: ffff8801cdcb20c0 R14: ffff8801cdcb1800 R15: dffffc0000000000
FS:  00007fcda7702700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000c42fc97010 CR3: 00000001bf292000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff8801cdcb1800
c ffff8801cdcb20c0
c 0000000200000003
c ffff8801cdcb1800
c
 ffffffff81624293
c dffffc0000000000
c ffff8801bdcc1dc8
c 000000000000000f
c
 ffff880182f870f0
c ffffffff812359eb
c 0000000000000010
c 0000000000000000
c
Call Trace:
 [<ffffffff812359eb>] __trace_hardirqs_on_caller kernel/locking/lockdep.c:2689 [inline]
 [<ffffffff812359eb>] trace_hardirqs_on_caller+0x38b/0x590 kernel/locking/lockdep.c:2736
 [<ffffffff81235bfd>] trace_hardirqs_on+0xd/0x10 kernel/locking/lockdep.c:2743
 [<ffffffff81624293>] lookup_bh_lru fs/buffer.c:1344 [inline]
 [<ffffffff81624293>] __find_get_block+0x183/0x4c0 fs/buffer.c:1356
 [<ffffffff81625159>] __getblk_slow fs/buffer.c:1101 [inline]
 [<ffffffff81625159>] __getblk_gfp+0x189/0x710 fs/buffer.c:1386
 [<ffffffff81628afd>] __bread_gfp+0x2d/0x270 fs/buffer.c:1420
 [<ffffffff818c4620>] sb_bread include/linux/buffer_head.h:300 [inline]
 [<ffffffff818c4620>] fat_ent_bread+0x160/0x2f0 fs/fat/fatent.c:106
 [<ffffffff818c631b>] fat_ent_read_block fs/fat/fatent.c:441 [inline]
 [<ffffffff818c631b>] fat_alloc_clusters+0x51b/0xe10 fs/fat/fatent.c:489
 [<ffffffff818d34ef>] fat_add_cluster+0x6f/0xe0 fs/fat/inode.c:100
 [<ffffffff818d383f>] __fat_get_block fs/fat/inode.c:147 [inline]
 [<ffffffff818d383f>] fat_get_block+0x2df/0x800 fs/fat/inode.c:176
 [<ffffffff81629d41>] __block_write_begin_int+0x391/0x1040 fs/buffer.c:1987
 [<ffffffff8162aa8f>] __block_write_begin fs/buffer.c:2038 [inline]
 [<ffffffff8162aa8f>] block_write_begin+0x5f/0x180 fs/buffer.c:2097
 [<ffffffff8162b0a3>] cont_write_begin+0x4f3/0x810 fs/buffer.c:2450
 [<ffffffff818cf9aa>] fat_write_begin+0x9a/0x120 fs/fat/inode.c:222
 [<ffffffff81435c91>] generic_perform_write+0x301/0x510 mm/filemap.c:2740
 [<ffffffff8143d66a>] __generic_file_write_iter+0x29a/0x540 mm/filemap.c:2833
 [<ffffffff8143dbf0>] generic_file_write_iter+0x2e0/0x610 mm/filemap.c:2893
 [<ffffffff8156ead0>] new_sync_write fs/read_write.c:496 [inline]
 [<ffffffff8156ead0>] __vfs_write+0x3e0/0x580 fs/read_write.c:509
 [<ffffffff815728c7>] vfs_write+0x187/0x530 fs/read_write.c:557
 [<ffffffff815766f9>] SYSC_write fs/read_write.c:604 [inline]
 [<ffffffff815766f9>] SyS_write+0xd9/0x1c0 fs/read_write.c:596
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f9b13>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 
cb8 
c00 
c00 
c00 
c41 
c8b 
c86 
cc0 
c08 
c00 
c00 
c85 
cc0 
c0f 
c8e 
c95 
c00 
c00 
c00 
c4c 
c8b 
c6d 
cc8 
c44 
c8d 
c24 
cb5 
c00 
c00 
c00 
c00 
c31 
cdb 
c49 
cbf 
c00 
c00 
c00 
c00 
c00 
cfc 
cff 
cdf 
c<41> 
c8d 
c44 
c24 
c02 
c89 
c45 
cd4 
c41 
c8d 
c44 
c24 
c03 
c89 
c45 
cd0 
c4d 
c8d 
ca6 
cc8 
c08 
c