KCSAN: data-race in p9_conn_cancel / p9_write_work

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 127c501a Merge tag '5.10-rc5-smb3-fixes' of git://git.samb..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1761897d500000
kernel config: https://syzkaller.appspot.com/x/.config?x=9b9b19d1bde60f8d
dashboard link: https://syzkaller.appspot.com/bug?extid=c359f69e8095f587c564
compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project.git 913f6005669cfb590c99865a90bc51ed0983d09d)
CC: [asma...@codewreck.org da...@davemloft.net eri...@gmail.com ku...@kernel.org linux-...@vger.kernel.org lu...@ionkov.net net...@vger.kernel.org v9fs-de...@lists.sourceforge.net]

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c359f6...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in p9_conn_cancel / p9_write_work

write to 0xffff8880407ca428 of 4 bytes by task 10791 on cpu 1:
p9_conn_cancel+0x88/0x400 net/9p/trans_fd.c:199
p9_poll_mux net/9p/trans_fd.c:626 [inline]
p9_poll_workfn+0x14c/0x410 net/9p/trans_fd.c:1143
process_one_work+0x3e1/0x950 kernel/workqueue.c:2272
worker_thread+0x635/0xb90 kernel/workqueue.c:2418
kthread+0x1fd/0x220 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

read to 0xffff8880407ca428 of 4 bytes by task 9763 on cpu 0:
p9_write_work+0x23/0x770 net/9p/trans_fd.c:449
process_one_work+0x3e1/0x950 kernel/workqueue.c:2272
worker_thread+0x635/0xb90 kernel/workqueue.c:2418
kthread+0x1fd/0x220 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 9763 Comm: kworker/0:4 Not tainted 5.10.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events p9_write_work
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.