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BUG: KCSAN: data-race in p9_conn_cancel / p9_poll_workfn

write to 0xffff88813b00a428 of 4 bytes by task 9 on cpu 0:
 p9_conn_cancel+0x89/0x400 net/9p/trans_fd.c:200
 p9_write_work+0x3ac/0x740 net/9p/trans_fd.c:523
 process_one_work+0x434/0x860 kernel/workqueue.c:2597
 worker_thread+0x5f2/0xa10 kernel/workqueue.c:2748
 kthread+0x1d7/0x210 kernel/kthread.c:389
 ret_from_fork+0x2e/0x40 arch/x86/kernel/process.c:145
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:296

read to 0xffff88813b00a428 of 4 bytes by task 20715 on cpu 1:
 p9_poll_mux net/9p/trans_fd.c:626 [inline]
 p9_poll_workfn+0xc0/0x410 net/9p/trans_fd.c:1167
 process_one_work+0x434/0x860 kernel/workqueue.c:2597
 worker_thread+0x5f2/0xa10 kernel/workqueue.c:2748
 kthread+0x1d7/0x210 kernel/kthread.c:389
 ret_from_fork+0x2e/0x40 arch/x86/kernel/process.c:145
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:296

value changed: 0x00000000 -> 0xffffff91

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 20715 Comm: kworker/1:1 Not tainted 6.5.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2023
Workqueue: events p9_poll_workfn
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