linux-kernel - Re: [RFC][PATCH 00/10] taskstats: Enhancements for precise accounting

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Date:	Fri, 24 Sep 2010 14:39:11 +0200
From:	Michael Holzheu <holzheu@...ux.vnet.ibm.com>
To:	Matt Helsley <matthltc@...ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Shailabh Nagar <nagar1234@...ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Venkatesh Pallipadi <venki@...gle.com>,
	John stultz <johnstul@...ibm.com>,
	containers@...ts.linux-foundation.org, linux-s390@...r.kernel.org,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: [RFC][PATCH 00/10] taskstats: Enhancements for precise
 accounting

Hello Matt,

On Thu, 2010-09-23 at 15:11 -0700, Matt Helsley wrote:
> > Talk to me about namespaces, please.  A lot of the new code involves
> > PIDs, but PIDs are not system-wide unique.  A PID is relative to a PID
> > namespace.  Does everything Just Work?  When userspace sends a PID to
> > the kernel, that PID is assumed to be within the sending process's PID
> > namespace?  If so, then please spell it all out in the changelogs.  If
> > not then that is a problem!
> 
> Good point.
> 
> The pid ought to be valid in the _receiving_ task's pid namespace. That
> can be difficult or impossible if we're talking about netlink broadcasts.
> In this regard process events connector is an example of what not to do.

I think that the netlink taskstats commands are executed in the context
of the calling process (at least my printk shows me that). The command
collects the process data using "current->nsproxy->pid_ns" and creates a
netlink reply. So everything should be fine here. Shouldn't it?

Hmmm, but for exit events, this might be broken in taskstats. The code
looks to me that every exiting task independent from the namespace is
reported as event via taskstat_exit(). Maybe I am missing something...

Michael



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