linux-kernel - Re: [PATCH 2/2] sched/deadline: Don't return invalid cpu in cpudl_maximum

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Date:   Wed, 7 Jun 2017 08:42:24 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     Juri Lelli <juri.lelli@....com>
CC:     <peterz@...radead.org>, <mingo@...nel.org>,
        <linux-kernel@...r.kernel.org>, <juri.lelli@...il.com>,
        <rostedt@...dmis.org>, <kernel-team@....com>
Subject: Re: [PATCH 2/2] sched/deadline: Don't return invalid cpu in
 cpudl_maximum_cpu()

On Tue, Jun 06, 2017 at 04:12:25PM +0100, Juri Lelli wrote:
> Hi,
> 
> On 02/06/17 16:31, Byungchul Park wrote:
> > When the heap tree is empty, cp->elements[0].cpu has meaningless value.

Hi,

The meaningless value is 0.

> > We need to consider the case.
> > 
> > Signed-off-by: Byungchul Park <byungchul.park@....com>
> > ---
> >  kernel/sched/cpudeadline.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
> > index d4a6963..9b314a9 100644
> > --- a/kernel/sched/cpudeadline.c
> > +++ b/kernel/sched/cpudeadline.c
> > @@ -110,7 +110,8 @@ static void cpudl_heapify(struct cpudl *cp, int idx)
> >  
> >  static inline int cpudl_maximum_cpu(struct cpudl *cp)
> >  {
> > -	return cp->elements[0].cpu;
> > +	int cpu = cp->elements[0].cpu;
> > +	return cp->elements[cpu].idx == IDX_INVALID ? -1 : cpu;
> 
> Mmm, don't we get a WARN from cpumask_check() if we return -1 here?

The function does not return -1 without my patch.

Right?

> 
> Thanks,
> 
> - Juri