procfs file open and read fail

Question

    proc_test = create_proc_entry("proc_test", S_IRUGO, NULL);
    if (proc_test) {
        proc_test->read_proc = _proc_read_test;
    }

A procfs file is created like the above, but sometimes it couldn't be read like the following.

$ ls -l /proc/proc_test
-r--r--r--    1 admin    admin           0 May 02 01:43 /proc/proc_test
$ cat /proc/proc_test
cat: can't open 'proc_test': No such file or directory
$ whoami
admin

It occurred once or twice of 100 times boot. How come it does?

What do I have to check more?