BUG: corrupted list in p9_fd_request

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: b5260801 Linux 4.14.140
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=15a5092e600000
kernel config: https://syzkaller.appspot.com/x/.config?x=a1845e2543d718e1
dashboard link: https://syzkaller.appspot.com/bug?extid=00bd306c64c69d4df709
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13787d9c600000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+00bd30...@syzkaller.appspotmail.com

8021q: adding VLAN 0 to HW filter on device batadv0
IPv6: ADDRCONF(NETDEV_UP): vxcan1: link is not ready
8021q: adding VLAN 0 to HW filter on device batadv0
list_add double add: new=ffff888097521098, prev=ffff888097521098,
next=ffff8880961877c0.
------------[ cut here ]------------
kernel BUG at lib/list_debug.c:29!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
Modules linked in:
kobject: '9p-95' (ffff88807fb9b6d0): kobject_uevent_env
CPU: 1 PID: 7028 Comm: syz-executor.3 Not tainted 4.14.140 #36
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
task: ffff88808d0fe480 task.stack: ffff88809c690000
RIP: 0010:__list_add_valid.cold+0x26/0x3c lib/list_debug.c:29
RSP: 0018:ffff88809c697a00 EFLAGS: 00010282
kobject: '9p-94' (ffff888094096e10): kobject_uevent_env
RAX: 0000000000000058 RBX: ffff888096187780 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff866d0ee0 RDI: ffffed10138d2f36
RBP: ffff88809c697a18 R08: 0000000000000058 R09: ffff88808d0fed48
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8880961877c0
R13: ffff888097521098 R14: ffff888097521098 R15: ffff888097521098
FS: 00007ff46c4ce700(0000) GS:ffff8880aef00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ff119ffe000 CR3: 000000008b88e000 CR4: 00000000001406e0
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+0xe3/0x2b0 net/9p/trans_fd.c:679
kobject: '9p-95' (ffff88807fb9b6d0): fill_kobj_path: path
= '/devices/virtual/bdi/9p-95'
p9_client_rpc+0x21b/0x1180 net/9p/client.c:774
kobject: '9p-94' (ffff888094096e10): fill_kobj_path: path
= '/devices/virtual/bdi/9p-94'
p9_client_clunk+0x89/0x150 net/9p/client.c:1507
v9fs_dentry_release+0x6d/0xd0 fs/9p/vfs_dentry.c:73
kobject: '9p-95' (ffff88807fb9b6d0): kobject_cleanup, parent
(null)
__dentry_kill+0x39a/0x580 fs/dcache.c:596
dentry_kill fs/dcache.c:632 [inline]
dput.part.0+0x59f/0x750 fs/dcache.c:847
dput fs/dcache.c:811 [inline]
do_one_tree+0x44/0x50 fs/dcache.c:1507
shrink_dcache_for_umount+0x67/0x140 fs/dcache.c:1521
generic_shutdown_super+0x6d/0x370 fs/super.c:431
kobject: '9p-94' (ffff888094096e10): kobject_cleanup, parent
(null)
kill_anon_super+0x3f/0x60 fs/super.c:1006
v9fs_kill_super+0x3e/0xa0 fs/9p/vfs_super.c:230
deactivate_locked_super+0x74/0xe0 fs/super.c:319
deactivate_super fs/super.c:350 [inline]
deactivate_super+0x85/0xa0 fs/super.c:346
cleanup_mnt+0xb2/0x150 fs/namespace.c:1183
__cleanup_mnt+0x16/0x20 fs/namespace.c:1190
task_work_run+0x114/0x190 kernel/task_work.c:113
kobject: '9p-95' (ffff88807fb9b6d0): calling ktype release
tracehook_notify_resume include/linux/tracehook.h:191 [inline]
exit_to_usermode_loop+0x1da/0x220 arch/x86/entry/common.c:164
prepare_exit_to_usermode arch/x86/entry/common.c:199 [inline]
syscall_return_slowpath arch/x86/entry/common.c:270 [inline]
do_syscall_64+0x4bc/0x640 arch/x86/entry/common.c:297
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x459879
RSP: 002b:00007ff46c4cdc78 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 0000000000000002 RCX: 0000000000459879
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 00000000200000c0
RBP: 000000000075bfc8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ff46c4ce6d4
kobject: '9p-94' (ffff888094096e10): calling ktype release
R13: 00000000004c902a R14: 00000000004e01b0 R15: 00000000ffffffff
Code: e9 56 ff ff ff 4c 89 e1 48 c7 c7 40 2c 9d 86
kobject: '9p-95': free name
e8 0f b8 72 fe 0f 0b 48 89 f2 4c 89 e1 4c 89 ee 48 c7 c7 80 2d 9d 86 e8 f8
b7 72 fe <0f> 0b 48
kobject: '9p-94': free name
89 f1 48 c7 c7 00 2d 9d 86 4c 89 e6 e8 e4 b7 72 fe 0f
RIP: __list_add_valid.cold+0x26/0x3c lib/list_debug.c:29 RSP:
ffff88809c697a00
kobject: 'loop1' (ffff8880a49c7220): kobject_uevent_env
---[ end trace 479d2f96a332ca4f ]---
kobject: '9p-98' (ffff888095464010): kobject_add_internal: parent: 'bdi',
set: 'devices'


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