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BUG: KCSAN: data-race in p9_conn_cancel / p9_fd_request

write to 0xffff88812bf18428 of 4 bytes by task 1915 on cpu 0:
 p9_conn_cancel+0x89/0x410 net/9p/trans_fd.c:201
 p9_poll_mux net/9p/trans_fd.c:631 [inline]
 p9_poll_workfn+0x14c/0x410 net/9p/trans_fd.c:1163
 process_one_work+0x3d3/0x720 kernel/workqueue.c:2289
 worker_thread+0x618/0xa70 kernel/workqueue.c:2436
 kthread+0x1a9/0x1e0 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306

read to 0xffff88812bf18428 of 4 bytes by task 3256 on cpu 1:
 p9_fd_request+0x2c/0x2a0 net/9p/trans_fd.c:673
 p9_client_rpc+0x1a5/0x6e0 net/9p/client.c:690
 p9_client_flush+0x194/0x230 net/9p/client.c:596
 p9_client_rpc+0x5e0/0x6e0 net/9p/client.c:724
 p9_client_attach+0xd5/0x350 net/9p/client.c:1096
 v9fs_session_init+0xb33/0xcf0 fs/9p/v9fs.c:457
 v9fs_mount+0x78/0x660 fs/9p/vfs_super.c:126
 legacy_get_tree+0x70/0xc0 fs/fs_context.c:610
 vfs_get_tree+0x49/0x190 fs/super.c:1531
 do_new_mount+0x200/0x650 fs/namespace.c:3040
 path_mount+0x4aa/0xb70 fs/namespace.c:3370
 do_mount fs/namespace.c:3383 [inline]
 __do_sys_mount fs/namespace.c:3591 [inline]
 __se_sys_mount+0x281/0x2d0 fs/namespace.c:3568
 __x64_sys_mount+0x63/0x70 fs/namespace.c:3568
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

value changed: 0x00000000 -> 0xffffff98

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 3256 Comm: syz-executor.3 Not tainted 6.1.0-rc4-syzkaller-00011-g59f2f4b8a757-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
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