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SubjectRe: [PATCH 2/5] softlockup: make detector be aware of task switch of processes hogging cpu
On Thu, Aug 21, 2014 at 09:37:04AM +0800, Chai Wen wrote:
> On 08/19/2014 09:36 AM, Chai Wen wrote:
>
> > On 08/19/2014 04:38 AM, Don Zickus wrote:
> >
> >> On Mon, Aug 18, 2014 at 09:02:00PM +0200, Ingo Molnar wrote:
> >>>
> >>> * Don Zickus <dzickus@redhat.com> wrote:
> >>>
> >>>>>>> So I agree with the motivation of this improvement, but
> >>>>>>> is this implementation namespace-safe?
> >>>>>>
> >>>>>> What namespace are you worried about colliding with? I
> >>>>>> thought softlockup_ would provide the safety?? Maybe I
> >>>>>> am missing something obvious. :-(
> >>>>>
> >>>>> I meant PID namespaces - a PID in itself isn't guaranteed
> >>>>> to be unique across the system.
> >>>>
> >>>> Ah, I don't think we thought about that. Is there a better
> >>>> way to do this? Is there a domain id or something that can
> >>>> be OR'd with the pid?
> >>>
> >>> What is always unique is the task pointer itself. We use pids
> >>> when we interface with user-space - but we don't really do that
> >>> here, right?
> >>
> >> No, I don't believe so. Ok, so saving 'current' and comparing that should
> >> be enough, correct?
> >>
> >
> >
> > I am not sure of the safety about using pid here with namespace.
> > But as to the pointer of process, is there a chance that we got a 'historical'
> > address saved in the 'softlockup_warn_pid(or address)_saved' and the current
> > hogging process happened to get the same task pointer address?
> > If it never happens, I think the comparing of address is ok.
> >
>
>
> Hi Ingo
>
> what do you think of Don's solution- 'comparing of task pointer' ?
> Anyway this is just an additional check about some very special cases,
> so I think the issue that I am concerned above is not a problem at all.
> And after learning some concepts about PID namespace, I think comparing
> of task pointer is reliable dealing with PID namespace here.
>
> And Don, If you want me to re-post this patch, please let me know that.

Sure, just quickly test with the task pointer to make sure it still works
and then re-post.

Cheers,
Don


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