page:ffffea0002dc8000 count:2 mapcount:0 mapping:          (null) index:0x0
flags: 0x4000000000004004(referenced|head)
page dumped because: VM_BUG_ON_PAGE(!PageLocked(page))
------------[ cut here ]------------
kernel BUG at mm/filemap.c:819!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 1 PID: 3708 Comm: syz-executor512 Not tainted 4.4.131-g3702e76 #38
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801cdba3000 task.stack: ffff8801ce0c8000
RIP: 0010:[<ffffffff8141de15>]  [<ffffffff8141de15>] unlock_page+0x115/0x150 mm/filemap.c:819
RSP: 0018:ffff8801ce0cf7d8  EFLAGS: 00010293
RAX: ffffffff83a6e7c0 RBX: ffffea0002dc8000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff81513249 RDI: ffff8801cdba38dc
RBP: ffff8801ce0cf7f8 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000001 R12: dffffc0000000000
R13: ffff8801ce0cfaa8 R14: ffffea0002dc9480 R15: ffffea0002dc8008
FS:  00007f9744b05700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000204a4ff0 CR3: 00000001cde19000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffea0002dc8000 dffffc0000000000 ffff8801ce0cfaa8 ffffea0002dc9480
 ffff8801ce0cf8e0 ffffffff812cc1bc 0000000000000001 ffff8801ce0cf890
 0000000000000046 ffff8800b19d6300 00000000cdba38d8 ffff8801ce0cfab8
Call Trace:
 [<ffffffff812cc1bc>] get_futex_key+0xadc/0xd80 kernel/futex.c:598
 [<ffffffff812cc999>] futex_wait_setup+0xd9/0x330 kernel/futex.c:2336
 [<ffffffff812cce9f>] futex_wait+0x2af/0x600 kernel/futex.c:2399
 [<ffffffff812d07b2>] do_futex+0x2a2/0x1770 kernel/futex.c:3186
 [<ffffffff812d1e70>] SYSC_futex kernel/futex.c:3246 [inline]
 [<ffffffff812d1e70>] SyS_futex+0x1f0/0x300 kernel/futex.c:3214
 [<ffffffff838bfd65>] entry_SYSCALL_64_fastpath+0x22/0x9e
Code: e8 48 8d 04 c0 49 8d 3c c6 e8 48 c0 df ff 5b 41 5c 41 5d 41 5e 5d c3 e8 da 33 f3 ff 48 c7 c6 60 aa a9 83 48 89 df e8 4b eb 06 00 <0f> 0b 48 89 df e8 f1 b1 0d 00 e9 0a ff ff ff e8 e7 b1 0d 00 e9 
RIP  [<ffffffff8141de15>] unlock_page+0x115/0x150 mm/filemap.c:819
 RSP <ffff8801ce0cf7d8>
---[ end trace 1e333039d710acc6 ]---