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

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Message-ID: <20180619060754.voy2nziqwl5ehfp5@unicorn.suse.cz>
Date:   Tue, 19 Jun 2018 08:07:55 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     linux-kernel@...r.kernel.org
Cc:     Alexey Dobriyan <adobriyan@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: regression: /proc/$pid/cmdline lacks trailing '\0' in 4.18-rc1

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