Infinite recursion turns into a D mode process

Question

Consider this program:

int w(int x, int y){
    if(x != y) {
        w(x, y);
    }else return x+y;
}

Call it this way:

w(0, 5);

For distinct values (like above), it generates an infinite recursion. The problem is, once the program started this way, the specific process turns into a D mode (waiting for an internal I/O, therefore untouchable).

Take a normal loop

while(1){
    if(0 != 5){
        //foo
    }else{
        //bar
    }
}

Generates R state mode - perfectly capable of getting SIGKILL.

Although normal loops beat recursions performance-wise; the system should still be capable of killing the process.

Why is this happening? And how to prevent it remotely?

The code will be compiled an executed by a program that returns its output to the webclient via sockets. So there is no control over what the user attempts to compile.

Edit:

Ubiquitous process of compiling and running the code:

$ g++ main.cpp -o m
$ ./m

Edit2:

$ g++ --version
g++ (GCC) 4.9.2 20150204 (prerelease)
Copyright (C) 2014 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ df --print-type
Filesystem     Type     1K-blocks      Used Available Use% Mounted on
/dev/sda2      ext4     957174124 168965980 739563400  19% /
dev            devtmpfs   4087124         0   4087124   0% /dev
run            tmpfs      4089872       528   4089344   1% /run
tmpfs          tmpfs      4089872        76   4089796   1% /dev/shm
tmpfs          tmpfs      4089872         0   4089872   0% /sys/fs/cgroup
tmpfs          tmpfs      4089872      1052   4088820   1% /tmp
tmpfs          tmpfs       817976        12    817964   1% /run/user/1000

The tests were done on Arch Linux x64 (with latest gcc).

Edit3:

The same problem occurs even after reinstalling the OS. The image has been used on another pc as well, where this problem does not occur.

Answer 1

I'm not sure to have undertood:

Launch your command in this way:

./m & echo $! > mpid

So to kill process:

kill $(cat mpid)