BUG: corrupted list in p9_fd_cancel

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    1e4b044d2251 Linux 4.18-rc4
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=156196a4400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=25856fac4e580aa7
dashboard link: https://syzkaller.appspot.com/bug?extid=735d926e9d1317c3310c
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
userspace arch: i386
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=12344f34400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1695badc400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+735d926e9d1317c3310c@xxxxxxxxxxxxxxxxxxxxxxxxx

list_del corruption, ffff8801aa15b2a8->next is LIST_POISON1  
(dead000000000100)
------------[ cut here ]------------
kernel BUG at lib/list_debug.c:47!
invalid opcode: 0000 [#1] SMP KASAN
CPU: 0 PID: 5039 Comm: syz-executor122 Not tainted 4.18.0-rc4+ #41
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:__list_del_entry_valid.cold.1+0x26/0x58 lib/list_debug.c:45
Code: 02 fe 0f 0b 4c 89 e2 48 89 de 48 c7 c7 a0 65 1a 88 e8 4a 6e 02 fe 0f  
0b 4c 89 ea 48 89 de 48 c7 c7 40 65 1a 88 e8 36 6e 02 fe <0f> 0b 48 89 de  
48 c7 c7 60 66 1a 88 e8 25 6e 02 fe 0f 0b 48 89 de
RSP: 0018:ffff8801cfeef180 EFLAGS: 00010286
RAX: 000000000000004e RBX: ffff8801aa15b2a8 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff81631821 RDI: 0000000000000001
RBP: ffff8801cfeef198 R08: ffff8801aac8e600 R09: ffffed003b5c4fc0
R10: ffffed003b5c4fc0 R11: ffff8801dae27e07 R12: dead000000000200
R13: dead000000000100 R14: ffff8801aa15b2a8 R15: ffff8801aa15b2b0
FS:  0000000000000000(0000) GS:ffff8801dae00000(0063) knlGS:00000000f7fe9b40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 0000000020000000 CR3: 00000001d8066000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 __list_del_entry include/linux/list.h:117 [inline]
 list_del include/linux/list.h:125 [inline]
 p9_fd_cancel+0x104/0x360 net/9p/trans_fd.c:690
 p9_client_rpc+0xf1f/0x1400 net/9p/client.c:800
 p9_client_version net/9p/client.c:976 [inline]
 p9_client_create+0xd09/0x16c9 net/9p/client.c:1069
 v9fs_session_init+0x21a/0x1a80 fs/9p/v9fs.c:400
 v9fs_mount+0x7c/0x900 fs/9p/vfs_super.c:135
 mount_fs+0xae/0x328 fs/super.c:1277
 vfs_kern_mount.part.34+0xdc/0x4e0 fs/namespace.c:1037
 vfs_kern_mount fs/namespace.c:1027 [inline]
 do_new_mount fs/namespace.c:2518 [inline]
 do_mount+0x581/0x30e0 fs/namespace.c:2848
 __do_compat_sys_mount fs/compat.c:125 [inline]
 __se_compat_sys_mount fs/compat.c:92 [inline]
 __ia32_compat_sys_mount+0x5d5/0x860 fs/compat.c:92
 do_syscall_32_irqs_on arch/x86/entry/common.c:326 [inline]
 do_fast_syscall_32+0x34d/0xfb2 arch/x86/entry/common.c:397
 entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7fedcb9
Code: 55 08 8b 88 64 cd ff ff 8b 98 68 cd ff ff 89 c8 85 d2 74 02 89 0a 5b  
5d c3 8b 04 24 c3 8b 1c 24 c3 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90  
90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 002b:00000000f7fe91ec EFLAGS: 00000286 ORIG_RAX: 0000000000000015
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000020002d00
RDX: 0000000020002d40 RSI: 0000000000200000 RDI: 0000000020002d80
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
Dumping ftrace buffer:
   (ftrace buffer empty)
---[ end trace 240dd2352208d421 ]---
RIP: 0010:__list_del_entry_valid.cold.1+0x26/0x58 lib/list_debug.c:45
Code: 02 fe 0f 0b 4c 89 e2 48 89 de 48 c7 c7 a0 65 1a 88 e8 4a 6e 02 fe 0f  
0b 4c 89 ea 48 89 de 48 c7 c7 40 65 1a 88 e8 36 6e 02 fe <0f> 0b 48 89 de  
48 c7 c7 60 66 1a 88 e8 25 6e 02 fe 0f 0b 48 89 de
RSP: 0018:ffff8801cfeef180 EFLAGS: 00010286
RAX: 000000000000004e RBX: ffff8801aa15b2a8 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff81631821 RDI: 0000000000000001
RBP: ffff8801cfeef198 R08: ffff8801aac8e600 R09: ffffed003b5c4fc0
R10: ffffed003b5c4fc0 R11: ffff8801dae27e07 R12: dead000000000200
R13: dead000000000100 R14: ffff8801aa15b2a8 R15: ffff8801aa15b2b0
FS:  0000000000000000(0000) GS:ffff8801dae00000(0063) knlGS:00000000f7fe9b40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 0000000020000000 CR3: 00000001d8066000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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