netdev - Re: [PATCH v4 0/3] Send audit/procinfo/cgroup data in socket-level control message

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Date:	Wed, 15 Jan 2014 18:21:43 -0500
From:	Eric Paris <eparis@...hat.com>
To:	David Miller <davem@...emloft.net>
Cc:	jkaluza@...hat.com, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, rgb@...hat.com, tj@...nel.org,
	lizefan@...wei.com, containers@...ts.linux-foundation.org,
	cgroups@...r.kernel.org, viro@...iv.linux.org.uk
Subject: Re: [PATCH v4 0/3] Send audit/procinfo/cgroup data in socket-level
 control message

On Wed, 2014-01-15 at 12:17 -0800, David Miller wrote:
> From: Jan Kaluza <jkaluza@...hat.com>
> Date: Mon, 13 Jan 2014 09:01:46 +0100
> 
> > Changes introduced in this patchset can also increase performance
> > of such server-like processes, because current way of opening and
> > parsing /proc/$PID/* files is much more expensive than receiving these
> > metadata using SCM.
> 
> The problem with this line of reasoning is that these changes will
> hurt everyone else, because these new control messages are sent
> unconditionally, whether the application is interested in them or not.
> 
> I really don't like this cost tradeoff, it's terrible, and therefore
> I'm really not inclined to apply these patches, sorry.

Agreed.  Although you seem to be ignoring the part of the logic where is
solves a problem that can not be solved today.

> The current practice to retrieve such process metadata is to look that
> information up in procfs with the $PID received over SCM_CREDENTIALS.
> This is sufficient for long-running tasks, but introduces a race which
> cannot be worked around for short-living processes; the calling
> process and all the information in /proc/$PID/ is gone before the
> receiver of the socket message can look it up.

Reliably being able to audit what process requested an action is
extremely useful.  And I like the audit patch, as it is a couple of ints
we are storing.

procinfo and cgroup can both be up to 4k of data.

Is there an alternative he should consider?  Some way to grab a
reference on task_struct and just attach that to the message?

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