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BUG: KCSAN: data-race in p9_conn_cancel / p9_fd_request

write to 0xffff8881571b9428 of 4 bytes by task 77 on cpu 0:
 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:1146
 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

read to 0xffff8881571b9428 of 4 bytes by task 6298 on cpu 1:
 p9_fd_request+0x2c/0x2a0 net/9p/trans_fd.c:668
 p9_client_rpc+0x14f/0x680 net/9p/client.c:746
 p9_client_flush+0x194/0x260 net/9p/client.c:664
 p9_client_rpc+0x57d/0x680 net/9p/client.c:780
 p9_client_version+0xa4/0x350
 p9_client_create+0x61b/0x7a0 net/9p/client.c:1056
 v9fs_session_init+0x100/0xcf0 fs/9p/v9fs.c:408
 v9fs_mount+0x57/0x510 fs/9p/vfs_super.c:126
 legacy_get_tree+0x70/0xc0 fs/fs_context.c:610
 vfs_get_tree+0x49/0x190 fs/super.c:1497
 do_new_mount+0x200/0x650 fs/namespace.c:3040
 path_mount+0x4b1/0xb60 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+0x44/0xae

value changed: 0x00000000 -> 0xffffff98

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 6298 Comm: syz-executor.3 Not tainted 5.18.0-rc2-syzkaller-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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