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BUG: KCSAN: data-race in p9_client_cb / p9_client_rpc

write to 0xffff88811ea8bf68 of 4 bytes by task 370 on cpu 0:
 p9_client_cb+0x14/0x40 net/9p/client.c:431
 p9_conn_cancel+0x3d0/0x460 net/9p/trans_fd.c:215
 p9_poll_mux net/9p/trans_fd.c:628 [inline]
 p9_poll_workfn+0x14c/0x410 net/9p/trans_fd.c:1145
 process_one_work+0x402/0x910 kernel/workqueue.c:2297
 worker_thread+0x636/0xae0 kernel/workqueue.c:2444
 kthread+0x262/0x280 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30

read to 0xffff88811ea8bf68 of 4 bytes by task 13089 on cpu 1:
 p9_client_rpc+0x398/0x660 net/9p/client.c:776
 p9_client_version+0xa0/0x310
 p9_client_create+0x631/0x720 net/9p/client.c:1057
 v9fs_session_init+0x100/0xd50 fs/9p/v9fs.c:406
 v9fs_mount+0x57/0x4c0 fs/9p/vfs_super.c:126
 legacy_get_tree+0x70/0xc0 fs/fs_context.c:610
 vfs_get_tree+0x4a/0x1a0 fs/super.c:1498
 do_new_mount fs/namespace.c:2988 [inline]
 path_mount+0x11ec/0x1d20 fs/namespace.c:3318
 do_mount fs/namespace.c:3331 [inline]
 __do_sys_mount fs/namespace.c:3539 [inline]
 __se_sys_mount+0x24b/0x2f0 fs/namespace.c:3516
 __x64_sys_mount+0x63/0x70 fs/namespace.c:3516
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00000002 -> 0x00000005

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 13089 Comm: syz-executor.0 Not tainted 5.15.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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