BUG: corrupted list in p9_write_work

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    116b181bb646 Add linux-next specific files for 20180803
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1333a3e0400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b4f38be7c2c519d5
dashboard link: https://syzkaller.appspot.com/bug?extid=1788bd5d4e051da6ec08
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+1788bd5d4e051da6ec08@xxxxxxxxxxxxxxxxxxxxxxxxx

list_add corruption. prev->next should be next (ffff8801c2aad370), but was  
ffff8801c2aad380. (prev=ffff8801b1a15ad8).
------------[ cut here ]------------
kernel BUG at lib/list_debug.c:28!
invalid opcode: 0000 [#1] SMP KASAN
CPU: 0 PID: 1879 Comm: kworker/0:2 Not tainted 4.18.0-rc7-next-20180803+ #31
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Workqueue: events p9_write_work
RIP: 0010:__list_add_valid.cold.0+0x23/0x25 lib/list_debug.c:26
Code: e8 4f ce 56 fe eb 97 48 89 d9 48 c7 c7 e0 9a 3a 87 e8 32 87 fe fd 0f  
0b 48 89 f1 48 c7 c7 a0 9b 3a 87 48 89 de e8 1e 87 fe fd <0f> 0b 4c 89 e2  
48 89 de 48 c7 c7 e0 9c 3a 87 e8 0a 87 fe fd 0f 0b
RSP: 0018:ffff8801ce447590 EFLAGS: 00010282
RAX: 0000000000000075 RBX: ffff8801c2aad370 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff816366f1 RDI: 0000000000000001
RBP: ffff8801ce4475a8 R08: ffff8801ce43a500 R09: ffffed003b604fd0
R10: ffffed003b604fd0 R11: ffff8801db027e87 R12: ffff8801b1a15ad8
R13: ffff8801b1a15ad8 R14: ffff8801c2aad3c4 R15: ffff8801b1a15ad8
FS:  0000000000000000(0000) GS:ffff8801db000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b31525000 CR3: 00000001b53b4000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 __list_add include/linux/list.h:60 [inline]
 list_add_tail include/linux/list.h:93 [inline]
 list_move_tail include/linux/list.h:183 [inline]
 p9_write_work+0x34e/0xd50 net/9p/trans_fd.c:470
 process_one_work+0xc73/0x1ba0 kernel/workqueue.c:2153
 worker_thread+0x189/0x13c0 kernel/workqueue.c:2296
 kthread+0x35a/0x420 kernel/kthread.c:246
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:415
Modules linked in:
Dumping ftrace buffer:
   (ftrace buffer empty)
---[ end trace fb8b29d28d8f9975 ]---
RIP: 0010:__list_add_valid.cold.0+0x23/0x25 lib/list_debug.c:26
Code: e8 4f ce 56 fe eb 97 48 89 d9 48 c7 c7 e0 9a 3a 87 e8 32 87 fe fd 0f  
0b 48 89 f1 48 c7 c7 a0 9b 3a 87 48 89 de e8 1e 87 fe fd <0f> 0b 4c 89 e2  
48 89 de 48 c7 c7 e0 9c 3a 87 e8 0a 87 fe fd 0f 0b
RSP: 0018:ffff8801ce447590 EFLAGS: 00010282
RAX: 0000000000000075 RBX: ffff8801c2aad370 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff816366f1 RDI: 0000000000000001
RBP: ffff8801ce4475a8 R08: ffff8801ce43a500 R09: ffffed003b604fd0
R10: ffffed003b604fd0 R11: ffff8801db027e87 R12: ffff8801b1a15ad8
R13: ffff8801b1a15ad8 R14: ffff8801c2aad3c4 R15: ffff8801b1a15ad8
FS:  0000000000000000(0000) GS:ffff8801db000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b31525000 CR3: 00000001b53b4000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxxx

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with  
syzbot.