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SubjectRe: [PATCH 04/14] hrtimer: use base->index instead of basenum in switch_hrtimer_base()
On Wed, 26 Mar 2014, Srivatsa S. Bhat wrote:
> On 03/26/2014 04:51 PM, Viresh Kumar wrote:
> > In switch_hrtimer_base() we have created a local variable basenum which is set
> > to base->index. This variable is used at only one place. It makes code more
> > readable if we remove this variable use base->index directly.
> >
>
> No, this doesn't look right. Note that the code can re-execute
> the assignment to new_base, by jumping to the 'again' label.
> See below.
>
> > --- a/kernel/hrtimer.c
> > +++ b/kernel/hrtimer.c
> > @@ -202,11 +202,10 @@ switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base,
> > struct hrtimer_cpu_base *new_cpu_base;
> > int this_cpu = smp_processor_id();
> > int cpu = get_nohz_timer_target(pinned);
> > - int basenum = base->index;
> >
> > again:
> > new_cpu_base = &per_cpu(hrtimer_bases, cpu);
> > - new_base = &new_cpu_base->clock_base[basenum];
> > + new_base = &new_cpu_base->clock_base[base->index];
> >
>
> Further down, timer->base can be altered (and set to NULL too).
> So if we jump back to 'again', we'll end up in trouble.
> So I think its important to cache the value in basenum and
> use it.

That's irrelevant. base is not changing.


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