regression: /proc/$pid/cmdline lacks trailing '\0' in 4.18-rc1

[Michal Kubecek]

In v4.18-rc1, /proc/$pid/cmdline is missing final null byte which used
to be there in v4.17 and older kernels:

4.17.1:
tweed:~ # cat /proc/self/cmdline | od -t c
0000000   c   a   t  \0   /   p   r   o   c   /   s   e   l   f   /   c
0000020   m   d   l   i   n   e  \0
0000027

4.18-rc1:
lion:~ # cat /proc/self/cmdline | od -t c
0000000   c   a   t  \0   /   p   r   o   c   /   s   e   l   f   /   c
0000020   m   d   l   i   n   e
0000026

The code has been rewritten quite a lot in 4.18-rc1 so I didn't find yet
where exactly does the change come from. Still looking.

Michal Kubecek