BUG: corrupted list in p9_fd_cancelled

[syzbot <syzbot+f78c15f5aa00e5c16d59@syzkaller.appspotmail.com>]

Hello,

syzbot found the following crash on:

HEAD commit:    1d4eb636f0ab Add linux-next specific files for 20180716
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=10abe770400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ea5926dddb0db97a
dashboard link: https://syzkaller.appspot.com/bug?extid=f78c15f5aa00e5c16d59
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+f78c15f5aa00e5c16d59@syzkaller.appspotmail.com

list_del corruption, ffff880193723368->next is LIST_POISON1  
(dead000000000100)
------------[ cut here ]------------
kernel BUG at lib/list_debug.c:47!
invalid opcode: 0000 [#1] SMP KASAN
CPU: 1 PID: 9124 Comm: syz-executor7 Not tainted 4.18.0-rc5-next-20180716+  
#8
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: ff fd 0f 0b 4c 89 e2 48 89 de 48 c7 c7 40 88 1a 88 e8 0a 35 ff fd 0f  
0b 4c 89 ea 48 89 de 48 c7 c7 e0 87 1a 88 e8 f6 34 ff fd <0f> 0b 48 89 de  
48 c7 c7 00 89 1a 88 e8 e5 34 ff fd 0f 0b 48 89 de
RSP: 0018:ffff88019b65f1d0 EFLAGS: 00010282
RAX: 000000000000004e RBX: ffff880193723368 RCX: ffffc90008c3b000
RDX: 0000000000000000 RSI: ffffffff81633fc1 RDI: 0000000000000001
RBP: ffff88019b65f1e8 R08: ffff88019918e100 R09: ffffed003b5e4fc0
R10: ffffed003b5e4fc0 R11: ffff8801daf27e07 R12: dead000000000200
R13: dead000000000100 R14: ffff8801ab908600 R15: dffffc0000000000
FS:  00007f238387e700(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000625208 CR3: 00000001b4588000 CR4: 00000000001406e0
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_cancelled+0x80/0x2f0 net/9p/trans_fd.c:707
  p9_client_flush+0x252/0x2a0 net/9p/client.c:693
  p9_client_rpc+0x122c/0x1400 net/9p/client.c:802
  p9_client_version net/9p/client.c:977 [inline]
  p9_client_create+0xdbc/0x177c net/9p/client.c:1070
  v9fs_session_init+0x21a/0x1a80 fs/9p/v9fs.c:400
  v9fs_mount+0x7c/0x900 fs/9p/vfs_super.c:135
  legacy_get_tree+0x118/0x440 fs/fs_context.c:659
  vfs_get_tree+0x1cb/0x5c0 fs/super.c:1743
  do_new_mount fs/namespace.c:2567 [inline]
  do_mount+0x6c1/0x1fb0 fs/namespace.c:2889
  ksys_mount+0x12d/0x140 fs/namespace.c:3105
  __do_sys_mount fs/namespace.c:3119 [inline]
  __se_sys_mount fs/namespace.c:3116 [inline]
  __x64_sys_mount+0xbe/0x150 fs/namespace.c:3116
  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x455ab9
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:00007f238387dc68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f238387e6d4 RCX: 0000000000455ab9
RDX: 00000000200002c0 RSI: 00000000200001c0 RDI: 0000000000000000
RBP: 000000000072bea0 R08: 00000000200003c0 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004c0201 R14: 00000000004cfe50 R15: 0000000000000000
Modules linked in:
Dumping ftrace buffer:
    (ftrace buffer empty)
---[ end trace 7de5f20f6f7cde43 ]---
RIP: 0010:__list_del_entry_valid.cold.1+0x26/0x58 lib/list_debug.c:45
Code: ff fd 0f 0b 4c 89 e2 48 89 de 48 c7 c7 40 88 1a 88 e8 0a 35 ff fd 0f  
0b 4c 89 ea 48 89 de 48 c7 c7 e0 87 1a 88 e8 f6 34 ff fd <0f> 0b 48 89 de  
48 c7 c7 00 89 1a 88 e8 e5 34 ff fd 0f 0b 48 89 de
serio: Serial port pts1
RSP: 0018:ffff88019b65f1d0 EFLAGS: 00010282
RAX: 000000000000004e RBX: ffff880193723368 RCX: ffffc90008c3b000
RDX: 0000000000000000 RSI: ffffffff81633fc1 RDI: 0000000000000001
RBP: ffff88019b65f1e8 R08: ffff88019918e100 R09: ffffed003b5e4fc0
R10: ffffed003b5e4fc0 R11: ffff8801daf27e07 R12: dead000000000200
R13: dead000000000100 R14: ffff8801ab908600 R15: dffffc0000000000
FS:  00007f238387e700(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000625208 CR3: 00000001b4588000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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