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BUG: KCSAN: data-race in p9_poll_workfn / p9_write_work

read to 0xffff8881190a1e58 of 4 bytes by task 3397 on cpu 1:
 p9_fd_poll net/9p/trans_fd.c:229 [inline]
 p9_poll_mux net/9p/trans_fd.c:630 [inline]
 p9_poll_workfn+0xeb/0x3e0 net/9p/trans_fd.c:1172
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0x4cb/0x9d0 kernel/workqueue.c:3319
 worker_thread+0x582/0x770 kernel/workqueue.c:3400
 kthread+0x486/0x510 kernel/kthread.c:464
 ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:153
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

write to 0xffff8881190a1e58 of 4 bytes by task 3679 on cpu 0:
 p9_fd_write net/9p/trans_fd.c:436 [inline]
 p9_write_work+0x5ae/0x720 net/9p/trans_fd.c:485
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0x4cb/0x9d0 kernel/workqueue.c:3319
 worker_thread+0x582/0x770 kernel/workqueue.c:3400
 kthread+0x486/0x510 kernel/kthread.c:464
 ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:153
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x00000000 -> 0x00000002

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3679 Comm: kworker/0:8 Not tainted 6.15.0-rc7-syzkaller-00152-gd0c22de9995b #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Workqueue: events p9_write_work
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