linux-kernel - Re: [PATCH] drivers: CCI: fix used_mask init in validate

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Date:	Thu, 09 Apr 2015 10:11:43 -0400
From:	Mark Salter <msalter@...hat.com>
To:	Mark Rutland <mark.rutland@....com>
Cc:	Will Deacon <Will.Deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] drivers: CCI: fix used_mask init in validate_group()

On Thu, 2015-04-09 at 14:51 +0100, Mark Rutland wrote:
> On Wed, Apr 08, 2015 at 07:21:24PM +0100, Mark Salter wrote:
> > Currently in validate_group(), there is a static initializer
> > for fake_pmu.used_mask which is based on CPU_BITS_NONE but
> > the used_mask array size is based on CCI_PMU_MAX_HW_EVENTS.
> > CCI_PMU_MAX_HW_EVENTS is not based on NR_CPUS, so CPU_BITS_NONE
> > is not correct and will cause a build failure if NR_CPUS
> > is set high enough to make CPU_BITS_NONE larger than used_mask.
> 
> Whoops. My bad.
> 
> > This patch changes the used_mask initialization to be runtime
> > based on the actual size of the array.
> > 
> > Signed-off-by: Mark Salter <msalter@...hat.com>
> > ---
> >  drivers/bus/arm-cci.c | 14 +++++++-------
> >  1 file changed, 7 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/bus/arm-cci.c b/drivers/bus/arm-cci.c
> > index 84fd660..1d83072 100644
> > --- a/drivers/bus/arm-cci.c
> > +++ b/drivers/bus/arm-cci.c
> > @@ -679,13 +679,13 @@ static int
> >  validate_group(struct perf_event *event)
> >  {
> >  	struct perf_event *sibling, *leader = event->group_leader;
> > -	struct cci_pmu_hw_events fake_pmu = {
> > -		/*
> > -		 * Initialise the fake PMU. We only need to populate the
> > -		 * used_mask for the purposes of validation.
> > -		 */
> > -		.used_mask = CPU_BITS_NONE,
> 
> Can we not simply change this to:
> 
> 		.used_mask = { 0 },
> 
> That should result in the entire array being zeroed.

It does, but it also causes the whole struct to be cleared.
With the memset, only used_mask gets cleared.


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