BUG: corrupted list in p9_fd_request

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    30c2c32d7f70 Merge tag 'drm-fixes-2018-07-10' of git://ano..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1776dac2400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=25856fac4e580aa7
dashboard link: https://syzkaller.appspot.com/bug?extid=47b2e3c10a15caedad75
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+47b2e3c10a15caedad75@xxxxxxxxxxxxxxxxxxxxxxxxx

list_add double add: new=ffff880195f68818, prev=ffff880195f68818,  
next=ffff8801d8b8ad40.
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x455c97
------------[ cut here ]------------
Code: 48
kernel BUG at lib/list_debug.c:31!
83
invalid opcode: 0000 [#1] SMP KASAN
c4
CPU: 0 PID: 6511 Comm: syz-executor1 Not tainted 4.18.0-rc4+ #140
08
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
48
RIP: 0010:__list_add_valid+0xaa/0xb0 lib/list_debug.c:29
89
Code:
d8
e8
5b
eb
5d
a9
c3
48
66
89 f7
0f
48
1f
89
84
75
00
e8
00
e8
00 00
61 52
00
59
48 89
fe
e8
48
48
8b
f7
75
d8
e8
48
eb bb
39
48
c3
89
0f
f2
92
48
c0
89
eb
d9
92
4c
66
89
90 b8
e6
10
48
00
c7
00
c7
00
60
0f
65 1a
05 <48>
88
3d
e8 7a
01
6f
f0 ff
02 fe
ff
<0f>
0f
0b 0f
83
1f 40
7d
00
bb fb
48 b8
ff
00
c3 66
00 00
2e
00 00
0f
fc ff
1f
df
84 00
55
00 00
48
00
89
e5
RSP: 002b:00007f836516da88 EFLAGS: 00000246
41 55
 ORIG_RAX: 0000000000000010
RSP: 0018:ffff88017fd573d0 EFLAGS: 00010282
RAX: ffffffffffffffda RBX: 00007f836516db30 RCX: 0000000000455c97
RAX: 0000000000000058 RBX: ffff8801d8b8ad40 RCX: ffffc90002236000
RDX: 0000000000000000 RSI: 0000000000004c01 RDI: 0000000000000016
RDX: 0000000000000000 RSI: ffffffff81631821 RDI: 0000000000000001
RBP: 0000000020000040 R08: 00007f836516db30 R09: 00007f836516dad0
RBP: ffff88017fd573e8 R08: ffff880191e48100 R09: ffffed003b5c4fc0
R10: ffffed003b5c4fc0 R11: ffff8801dae27e07 R12: ffff880195f68818
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000015
R13: ffff880199a8ee00 R14: ffff880195f687f0 R15: ffff880195f68818
FS:  00007f8135acb700(0000) GS:ffff8801dae00000(0000) knlGS:0000000000000000
R13: 0000000000000000 R14: 00000000004d3e38 R15: 0000000000000028
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffdb706a040 CR3: 00000001aa239000 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]
 p9_fd_request+0x145/0x440 net/9p/trans_fd.c:667
 p9_client_rpc+0x290/0x1400 net/9p/client.c:768
 p9_client_clunk+0x93/0x180 net/9p/client.c:1488
 v9fs_dentry_release+0x68/0xd0 fs/9p/vfs_dentry.c:73
 __dentry_kill+0x4c0/0x7a0 fs/dcache.c:573
 dentry_kill+0xc9/0x5a0 fs/dcache.c:687
 dput.part.26+0x66b/0x7a0 fs/dcache.c:848
 dput fs/dcache.c:831 [inline]
 do_one_tree+0x37/0x40 fs/dcache.c:1531
 shrink_dcache_for_umount+0xc7/0x2b0 fs/dcache.c:1545
 generic_shutdown_super+0xd5/0x530 fs/super.c:438
 kill_anon_super+0x3c/0x50 fs/super.c:1046
 v9fs_kill_super+0x3e/0xa0 fs/9p/vfs_super.c:230
 deactivate_locked_super+0x97/0x100 fs/super.c:326
 deactivate_super+0x193/0x1c0 fs/super.c:357
 cleanup_mnt+0xbf/0x160 fs/namespace.c:1174
 __cleanup_mnt+0x16/0x20 fs/namespace.c:1181
 task_work_run+0x1ec/0x2a0 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:192 [inline]
 exit_to_usermode_loop+0x313/0x370 arch/x86/entry/common.c:166
 prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
 do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x455e29
Code: 1d ba fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7  
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 eb b9 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f8135acac68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 00007f8135acb6d4 RCX: 0000000000455e29
RDX: 0000000000000000 RSI: 0000000000000003 RDI: 00000000200002c0
RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004c2aa8 R14: 00000000004d4510 R15: 0000000000000000
Modules linked in:
Dumping ftrace buffer:
   (ftrace buffer empty)
---[ end trace dfed325e11645735 ]---
RIP: 0010:__list_add_valid+0xaa/0xb0 lib/list_debug.c:29
Code: e8 eb a9 48 89 f7 48 89 75 e8 e8 61 52 59 fe 48 8b 75 e8 eb bb 48 89  
f2 48 89 d9 4c 89 e6 48 c7 c7 60 65 1a 88 e8 7a 6f 02 fe <0f> 0b 0f 1f 40  
00 48 b8 00 00 00 00 00 fc ff df 55 48 89 e5 41 55
RSP: 0018:ffff88017fd573d0 EFLAGS: 00010282
RAX: 0000000000000058 RBX: ffff8801d8b8ad40 RCX: ffffc90002236000
RDX: 0000000000000000 RSI: ffffffff81631821 RDI: 0000000000000001
RBP: ffff88017fd573e8 R08: ffff880191e48100 R09: ffffed003b5c4fc0
R10: ffffed003b5c4fc0 R11: ffff8801dae27e07 R12: ffff880195f68818
R13: ffff880199a8ee00 R14: ffff880195f687f0 R15: ffff880195f68818
FS:  00007f8135acb700(0000) GS:ffff8801dae00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffdb706a040 CR3: 00000001aa239000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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