general protection fault in p9_conn_cancel

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 9e790395 Merge 4.9.112 into android-4.9
git tree: android-4.9
console output: https://syzkaller.appspot.com/x/log.txt?x=150bbd94400000
kernel config: https://syzkaller.appspot.com/x/.config?x=426e5da9eb2ee17a
dashboard link: https://syzkaller.appspot.com/bug?extid=601cb6ecf98aaa9c900b
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=134d4394400000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=117a712c400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+601cb6...@syzkaller.appspotmail.com

kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
(ftrace buffer empty)
Modules linked in:
CPU: 1 PID: 25 Comm: kworker/1:1 Not tainted 4.9.112-g9e79039 #7
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Workqueue: events p9_poll_workfn
task: ffff8801d9aec800 task.stack: ffff8801d9428000
RIP: 0010:[<ffffffff81236beb>] [<ffffffff81236beb>]
__lock_acquire+0xa1b/0x4070 kernel/locking/lockdep.c:3224
RSP: 0018:ffff8801d942f8e0 EFLAGS: 00010006
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000003 RSI: 0000000000000000 RDI: 0000000000000018
RBP: ffff8801d942fa90 R08: 0000000000000001 R09: 0000000000000001
R10: ffff8801d9aec800 R11: 0000000000000001 R12: 0000000000000001
R13: 0000000000000000 R14: 0000000000000018 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000046b5d0 CR3: 00000001cc939000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
0000000041b58ab3 ffff8801d9aed0f0 0000000000000002 0000000000000001
0000000000000000 ffff8801d9aed112 ffff8801d942fad0 0000000000000046
0000000000000000 ffff8801d9aed0ea ffff8801d942fae8 0000000000000046
Call Trace:
[<ffffffff8123acb0>] lock_acquire+0x130/0x3e0 kernel/locking/lockdep.c:3756
[<ffffffff839f9e9e>] __raw_spin_lock_irqsave
include/linux/spinlock_api_smp.h:112 [inline]
[<ffffffff839f9e9e>] _raw_spin_lock_irqsave+0x4e/0x62
kernel/locking/spinlock.c:159
[<ffffffff839c2b5a>] p9_conn_cancel+0xaa/0x4c0 net/9p/trans_fd.c:201
[<ffffffff839c34c2>] p9_poll_mux net/9p/trans_fd.c:630 [inline]
[<ffffffff839c34c2>] p9_poll_workfn+0x222/0x330 net/9p/trans_fd.c:1097
[<ffffffff8118d191>] process_one_work+0x7e1/0x1500 kernel/workqueue.c:2092
[<ffffffff8118df86>] worker_thread+0xd6/0x10a0 kernel/workqueue.c:2226
[<ffffffff8119d0bd>] kthread+0x26d/0x300 kernel/kthread.c:211
[<ffffffff839fa11c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Code: 25 28 00 00 00 0f 85 17 27 00 00 48 8d 65 d8 5b 41 5c 41 5d 41 5e 41
5f 5d c3 48 b8 00 00 00 00 00 fc ff df 4c 89 f2 48 c1 ea 03 <80> 3c 02 00
0f 85 51 27 00 00 49 81 3e a0 8c e9 84 0f 84 08 f7
RIP [<ffffffff81236beb>] __lock_acquire+0xa1b/0x4070
kernel/locking/lockdep.c:3224
RSP <ffff8801d942f8e0>
---[ end trace e63856aea98d1302 ]---


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