Re: [PATCH 04/14] hrtimer: use base->index instead of basenum in switch_hrtimer_base()

[Thomas Gleixner]

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.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/