Re: pid namespace isolation broken with powertop

[Nathan Lynch <ntl-e+AXbWqSrlAAvxtiuMwx3w@public.gmane.org>]

On Thu, 2010-07-29 at 14:30 +0200, Daniel Lezcano wrote:
> Hi all,
> 
> I noticed all the tasks of the host are listed in /proc/timer_stats
> These information is not virtualized neither isolated within a container.
> 
> I was expecting to see only the tasks in the container with the 
> corresponding pids.
> 
> I am not sure this is something critical, but the usage of powertop in 
> the container shows all the tasks of the system.
> 
> While looking at the code in kernel/time/timer.c, it is not obvious to 
> fix this isolation because it is the pid number which is stored in a 
> list, so there is not enough informations to discriminate the pid 
> namespace against the current one.
> 
> I am wondering if:
> 
>   1) is it worth to isolate these informations ? (IMHO, yes).
>   2) should the stats be stored per pid namespace or adding an hash 
> value + pid namespace as a key in the timer stats list ?

Well, powertop is used for monitoring and modifying global system
characteristics (e.g. processor C states, USB autosuspend) that don't
make sense to virtualize.  Many events in /proc/timer_stats are
accocunted to pid 0 (swapper/idle).  I think the question is whether a
pidns-relative slice of timer events will be useful or just confusing.