Re: [PATCH] perf/arm-dmc620: Fix lockdep assert in ->event_init()

[Robin Murphy]

On 17/05/2024 1:02 pm, Will Deacon wrote:
> On Tue, May 14, 2024 at 11:00:50AM -0700, Namhyung Kim wrote:
> > for_each_sibling_event() checks leader's ctx but it doesn't have the ctx
> > yet if it's the leader.  Like in perf_event_validate_size(), we should
> > skip checking siblings in that case.
> >
> > Fixes: f3c0eba287049 ("perf: Add a few assertions")
> > Reported-by: Greg Thelen <gthelen@xxxxxxxxxx>
> > Cc: Robin Murphy <robin.murphy@xxxxxxx>
> > Cc: Tuan Phan <tuanphan@xxxxxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
> > ---
> >   drivers/perf/arm_dmc620_pmu.c | 9 ++++++---
> >   1 file changed, 6 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/perf/arm_dmc620_pmu.c b/drivers/perf/arm_dmc620_pmu.c
> > index 8a81be2dd5ec..88c17c1d6d49 100644
> > --- a/drivers/perf/arm_dmc620_pmu.c
> > +++ b/drivers/perf/arm_dmc620_pmu.c
> > @@ -542,12 +542,16 @@ static int dmc620_pmu_event_init(struct perf_event *event)
> >   	if (event->cpu < 0)
> >   		return -EINVAL;
> >   
> > +	hwc->idx = -1;
> > +
> > +	if (event->group_leader == event)
> > +		return 0;
> > +
> >   	/*
> >   	 * We can't atomically disable all HW counters so only one event allowed,
> >   	 * although software events are acceptable.
> >   	 */
> > -	if (event->group_leader != event &&
> > -			!is_software_event(event->group_leader))
> > +	if (!is_software_event(event->group_leader))
> >   		return -EINVAL;

Oh, come to think of it, I believe we shouldn't actually need to keep 
this check either, since commit bf480f938566 ("perf/core: Don't allow 
grouping events from different hw pmus").

Thanks,
Robin.

> >   
> >   	for_each_sibling_event(sibling, event->group_leader) {
> > @@ -556,7 +560,6 @@ static int dmc620_pmu_event_init(struct perf_event *event)
> >   			return -EINVAL;
> >   	}
> >   
> > -	hwc->idx = -1;
> >   	return 0;
> >   }
>
> Thanks, I'll pick this up, although Mark reckoned he'd found some other
> issues over at:
>
> https://lore.kernel.org/r/Zg0l642PgQ7T3a8Z@FVFF77S0Q05N
>
> but didn't elaborate on what exactly he'd found :/
>
> Will
>
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