Re: Latency histogram broken after "hrtimer: Set expiry time before switch_hrtimer_base()"

[Carsten Emde]

On 06/22/2014 06:24 AM, Mike Galbraith wrote:
> [..]
> On Sun, 2014-06-22 at 06:10 +0200, Mike Galbraith wrote:
> > On Sun, 2014-06-22 at 02:04 +0100, Ben Hutchings wrote:
> > > In an rt-kernel with CONFIG_MISSED_TIMER_OFFSETS_HIST enabled,
> > > __hrtimer_start_range_ns() now crashes, as new_base is not assigned
> > > before it is used.
> >
> > Oh yeah, forgot about this.
> >
> > > I'm not sure how this should be fixed; is it:
> >
> > My (3.12-ish tree) merge resolution was the later, but it shouldn't
> > matter which you choose, what's stored where is unchanged pre/post.
I can confirm that 3.12.22-rt34 systems with 
CONFIG_MISSED_TIMER_OFFSETS_HIST enabled crash at an early boot stage. 
After applying Ben's second patch proposal, all is back to normal.

> > > --- a/kernel/hrtimer.c
> > > +++ b/kernel/hrtimer.c
> > > @@ -1108,7 +1108,7 @@ int __hrtimer_start_range_ns(struct hrti
> > >
> > >   #ifdef CONFIG_MISSED_TIMER_OFFSETS_HIST
> > >   	{
> > > -		ktime_t now = new_base->get_time();
> > > +		ktime_t now = base->get_time();
> > >
> > >   		if (ktime_to_ns(tim) < ktime_to_ns(now))
> > >   			timer->praecox = now;
> > > --- END ---
> > >
> > > or:
Didn't use this one.

> > > --- a/kernel/hrtimer.c
> > > +++ b/kernel/hrtimer.c
> > > @@ -1106,6 +1106,11 @@ int __hrtimer_start_range_ns(struct hrti
> > >   #endif
> > >   	}
> > >
> > > +	hrtimer_set_expires_range_ns(timer, tim, delta_ns);
> > > +
> > > +	/* Switch the timer base, if necessary: */
> > > +	new_base = switch_hrtimer_base(timer, base, mode & HRTIMER_MODE_PINNED);
> > > +
> > >   #ifdef CONFIG_MISSED_TIMER_OFFSETS_HIST
> > >   	{
> > >   		ktime_t now = new_base->get_time();
> > > @@ -1117,11 +1122,6 @@ int __hrtimer_start_range_ns(struct hrti
> > >   	}
> > >   #endif
> > >
> > > -	hrtimer_set_expires_range_ns(timer, tim, delta_ns);
> > > -
> > > -	/* Switch the timer base, if necessary: */
> > > -	new_base = switch_hrtimer_base(timer, base, mode & HRTIMER_MODE_PINNED);
> > > -
> > >   	timer_stats_hrtimer_set_start_info(timer);
> > >
> > >   	leftmost = enqueue_hrtimer(timer, new_base);
> > > --- END ---
> > > or something else?
Tested-by: Carsten Emde <C.Emde@xxxxxxxxx>

Thanks,
	-Carsten.
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