RE: [PATCH v3 1/2] cputime: fix invalid gtime in proc

Hiroshi Shimamoto
2015-11-10T08:45:01Z

> Subject: Re: [PATCH v3 1/2] cputime: fix invalid gtime in proc
>
> On Mon, Nov 02, 2015 at 05:13:51PM +0100, Peter Zijlstra wrote:
> > On Fri, Oct 30, 2015 at 12:46:39AM +0000, Hiroshi Shimamoto wrote:
> > > +++ b/kernel/sched/cputime.c
> > > @@ -786,6 +786,9 @@ cputime_t task_gtime(struct task_struct *t)
> > > unsigned int seq;
> > > cputime_t gtime;
> > >
> > > + if (!context_tracking_is_enabled())
> > > + return t->gtime;
> > > +
> >
> > Yeah, not happy about that.. why do we have to touch context tracking
> > muck to find vtime state etc.
>
> That's right, this is because it is deemed to be a quick and non invasive fix
> to be backported.
>
> Then will come the more invasive but proper fix consisting in having
> vtime_accounting_enabled() telling if vtime is running on any CPU and
> vtime_accounting_cpu_enabled(). The first will be used for remote readers
> (as in this patch) and the second for writers.
>
> Since we are dealing with a regression, it's better to minimize the changes.
> AFAICT, the regression got introduced in 2012:
>
> 6a61671bb2f3a1bd12cd17b8fca811a624782632
> ("cputime: Safely read cputime of full dynticks CPUs")

Is this patch going to apply to fix the regression?

thanks,
Hiroshi

>
> >
> > > do {
> > > seq = read_seqbegin(&t->vtime_seqlock);
> > >
> > > --
> > > 1.8.3.1
> > >