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Re: [RFC PATCH 1/4] Minimally invasive deadline wrap-around bugfix for SCHED_DEADLINE cpu heap

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  Re: [RFC PATCH 1/4] Minimally invasive deadline wrap-around bugfix  for SCHED_DEADLINE cpu heap Juri Lelli <juri.lelli@arm.com> - 2016-08-01 14:00 +0200
    Re: [RFC PATCH 1/4] Minimally invasive deadline wrap-around bugfix  for SCHED_DEADLINE cpu heap Juri Lelli <juri.lelli@arm.com> - 2016-08-01 15:00 +0200

#1453163 — Re: [RFC PATCH 1/4] Minimally invasive deadline wrap-around bugfix for SCHED_DEADLINE cpu heap

Hi,

On 19/07/16 11:44, Tommaso Cucinotta wrote:
> Current code in cpudeadline.c has a bug in re-heapifying when adding a
> new element at the end of the heap, because a deadline value of 0 is
> temporarily set in the new elem, then cpudl_change_key() is called
> with the actual elem deadline as param. However, the function compares
> the new deadline to set with the one previously in the elem, which is
> 0.  So, if current absolute deadlines grew so much to have negative
> values as s64, the comparison in cpudl_change_key() makes the wrong
> decision.  Instead, as from dl_time_before(), the kernel should handle
> correctly abs deadlines wrap-arounds.
> 
> This patch fixes the problem with a minimally invasive change that
> forces cpudl_change_key() to heapify up in this case.
> 
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Juri Lelli <juri.lelli@arm.com>
> Cc: Luca Abeni <luca.abeni@unitn.it>
> Reviewed-by: Luca Abeni <luca.abeni@unitn.it>
> Signed-off-by: Tommaso Cucinotta <tommaso.cucinotta@sssup.it>
> ---
>  kernel/sched/cpudeadline.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
> index 5be5882..d418449 100644
> --- a/kernel/sched/cpudeadline.c
> +++ b/kernel/sched/cpudeadline.c
> @@ -168,7 +168,7 @@ void cpudl_set(struct cpudl *cp, int cpu, u64 dl, int is_valid)
>  
>  	if (old_idx == IDX_INVALID) {
>  		cp->size++;
> -		cp->elements[cp->size - 1].dl = 0;
> +		cp->elements[cp->size - 1].dl = dl;
>  		cp->elements[cp->size - 1].cpu = cpu;
>  		cp->elements[cpu].idx = cp->size - 1;
>  		cpudl_change_key(cp, cp->size - 1, dl);

Looks good. I'd only change the subject to something like:

 sched/deadline: Wrap-around bugfix for cpu heap

Best,

- Juri

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#1453192

On 01/08/16 12:43, Juri Lelli wrote:
> Hi,
> 
> On 19/07/16 11:44, Tommaso Cucinotta wrote:
> > Current code in cpudeadline.c has a bug in re-heapifying when adding a
> > new element at the end of the heap, because a deadline value of 0 is
> > temporarily set in the new elem, then cpudl_change_key() is called
> > with the actual elem deadline as param. However, the function compares
> > the new deadline to set with the one previously in the elem, which is
> > 0.  So, if current absolute deadlines grew so much to have negative
> > values as s64, the comparison in cpudl_change_key() makes the wrong
> > decision.  Instead, as from dl_time_before(), the kernel should handle
> > correctly abs deadlines wrap-arounds.
> > 
> > This patch fixes the problem with a minimally invasive change that
> > forces cpudl_change_key() to heapify up in this case.
> > 
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Juri Lelli <juri.lelli@arm.com>
> > Cc: Luca Abeni <luca.abeni@unitn.it>
> > Reviewed-by: Luca Abeni <luca.abeni@unitn.it>
> > Signed-off-by: Tommaso Cucinotta <tommaso.cucinotta@sssup.it>
> > ---
> >  kernel/sched/cpudeadline.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
> > index 5be5882..d418449 100644
> > --- a/kernel/sched/cpudeadline.c
> > +++ b/kernel/sched/cpudeadline.c
> > @@ -168,7 +168,7 @@ void cpudl_set(struct cpudl *cp, int cpu, u64 dl, int is_valid)
> >  
> >  	if (old_idx == IDX_INVALID) {
> >  		cp->size++;
> > -		cp->elements[cp->size - 1].dl = 0;
> > +		cp->elements[cp->size - 1].dl = dl;
> >  		cp->elements[cp->size - 1].cpu = cpu;
> >  		cp->elements[cpu].idx = cp->size - 1;
> >  		cpudl_change_key(cp, cp->size - 1, dl);
> 
> Looks good. I'd only change the subject to something like:
> 
>  sched/deadline: Wrap-around bugfix for cpu heap
> 

and please remove linux-dl mailing list from future postings. It's
subscribers only, and practically dead (AFAIK).

Thanks,

- Juri

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