linux-kernel - Re: + pid-delete-reserved_pids.patch added to -mm tree

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Date:   Wed, 4 Oct 2017 00:53:49 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     akpm@...ux-foundation.org, ebiederm@...ssion.com,
        keescook@...omium.org, mm-commits@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: + pid-delete-reserved_pids.patch added to -mm tree

On Tue, Oct 03, 2017 at 05:53:15PM +0200, Oleg Nesterov wrote:
> On 10/02, Andrew Morton wrote:
> >
> > From: Alexey Dobriyan <adobriyan@...il.com>
> > Subject: pid: delete RESERVED_PIDS
> >
> > RESERVED_PIDS had a noble goal: to protect root from PID exhaustion since
> > at least ~2.5.40
> 
> I am just curious, where did you find the change which documents this goal?

Now that you asked, I'm not exactly sure. :-( Please don't tell it is for some
kind of stupid userspace which assumed low numbers are kernel threads.

> > except it never did that because there was no capability
> > or uid checks.
> >
> > Allow small pids to be allocated after rollover, there is nothing sacred
> > about them.
> >
> > Resource exhaustion should be handled by rlimits and/or kernel memory
> > accounting.
> 
> I won't argue, but I always thought that the only purpose of RESERVED_PIDS
> is to make the system/kernek daemons started at boot time more "visible" in
> /usr/bin/ps output.

They will be first in line naturally: kthreadd + init execute first and
rarely exit.