list_del corruption. prev->next should be ffff8801c75a70d0, but was ffff8801c74c9140
------------[ cut here ]------------
kernel BUG at lib/list_debug.c:53!
invalid opcode: 0000 [#1] SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 2807 Comm: syz-executor4 Not tainted 4.13.0-rc7-next-20170901+ #13
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801c553c300 task.stack: ffff8801c75a0000
RIP: 0010:__list_del_entry_valid+0xef/0x150 lib/list_debug.c:51
RSP: 0018:ffff8801c75a6e90 EFLAGS: 00010286
RAX: 0000000000000054 RBX: ffff8801ce39fa80 RCX: 0000000000000000
RDX: 0000000000000054 RSI: ffffffff81588fbe RDI: ffffed0038eb4dc6
RBP: ffff8801c75a6ea8 R08: ffff8801c75a6580 R09: 0000000000000000
R10: ffff8801c75a6778 R11: 0000000000000000 R12: ffff8801ce39fa80
R13: dffffc0000000000 R14: ffff8801c82c1e00 R15: ffff8801c75a70d8
FS:  00007f40eab37700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000a6f918 CR3: 00000001cb574000 CR4: 00000000001406f0
Call Trace:
 __list_del_entry include/linux/list.h:116 [inline]
 list_del include/linux/list.h:124 [inline]
 __remove_wait_queue include/linux/wait.h:182 [inline]
 userfaultfd_event_wait_completion+0x519/0x910 fs/userfaultfd.c:591
 dup_fctx fs/userfaultfd.c:687 [inline]
 dup_userfaultfd_complete+0x2de/0x480 fs/userfaultfd.c:695
 dup_mmap kernel/fork.c:726 [inline]
 dup_mm kernel/fork.c:1179 [inline]
 copy_mm+0xe9b/0x1310 kernel/fork.c:1233
 copy_process.part.36+0x1eae/0x4af0 kernel/fork.c:1735
 copy_process kernel/fork.c:1548 [inline]
 _do_fork+0x1ef/0xfe0 kernel/fork.c:2027
 SYSC_clone kernel/fork.c:2137 [inline]
 SyS_clone+0x37/0x50 kernel/fork.c:2131
 do_syscall_64+0x26c/0x8c0 arch/x86/entry/common.c:287
 entry_SYSCALL64_slow_path+0x25/0x25
RIP: 0033:0x451e59
RSP: 002b:00007f40eab36c08 EFLAGS: 00000216 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 0000000000718000 RCX: 0000000000451e59
RDX: 000000002003b000 RSI: 0000000020038f62 RDI: 0000000020000000
RBP: 00000000000003e0 R08: 0000000020057000 R09: 0000000000000000
R10: 0000000020023ffc R11: 0000000000000216 R12: 00000000004b717a
R13: 00000000ffffffff R14: 0000000020000000 R15: 0000000020038f62
Code: 4c 89 e2 48 c7 c7 c0 d0 fd 84 e8 42 75 1a ff 0f 0b 48 c7 c7 20 d1 fd 84 e8 34 75 1a ff 0f 0b 48 c7 c7 80 d1 fd 84 e8 26 75 1a ff <0f> 0b 48 c7 c7 e0 d1 fd 84 e8 18 75 1a ff 0f 0b 48 89 df 48 89 
RIP: __list_del_entry_valid+0xef/0x150 lib/list_debug.c:51 RSP: ffff8801c75a6e90
---[ end trace 3bc7c0422801993b ]---
Kernel panic - not syncing: Fatal exception
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..