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BUG: KCSAN: data-race in p9_poll_workfn / p9_write_work

write to 0xffff88811621a89c of 4 bytes by task 3196 on cpu 1:
 p9_write_work+0x42c/0x750 net/9p/trans_fd.c:498
 process_one_work kernel/workqueue.c:3231 [inline]
 process_scheduled_works+0x483/0x9a0 kernel/workqueue.c:3312
 worker_thread+0x526/0x730 kernel/workqueue.c:3393
 kthread+0x1d1/0x210 kernel/kthread.c:389
 ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

read to 0xffff88811621a89c of 4 bytes by task 23995 on cpu 0:
 p9_poll_mux net/9p/trans_fd.c:646 [inline]
 p9_poll_workfn+0x2bf/0x420 net/9p/trans_fd.c:1177
 process_one_work kernel/workqueue.c:3231 [inline]
 process_scheduled_works+0x483/0x9a0 kernel/workqueue.c:3312
 worker_thread+0x526/0x730 kernel/workqueue.c:3393
 kthread+0x1d1/0x210 kernel/kthread.c:389
 ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

value changed: 0x00000009 -> 0x00000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 23995 Comm: kworker/0:5 Not tainted 6.9.0-syzkaller-08995-g0450d2083be6 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024
Workqueue: events p9_poll_workfn
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