linux-kernel - Re: [PATCH] perf/arm-smmuv3: Fix lockdep assert in ->event

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Message-ID: <CAJpZYjWy_c=Yhs-YnMyUM0BJvjmUGE57FTu66iSf3E02vObyyQ@mail.gmail.com>
Date: Thu, 7 Nov 2024 21:09:53 -0800
From: Chun-Tse Shao <ctshao@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: linux-kernel@...r.kernel.org, Greg Thelen <gthelen@...gle.com>, 
	Robin Murphy <robin.murphy@....com>, Tuan Phan <tuanphan@...amperecomputing.com>, 
	Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Peter Zijlstra <peterz@...radead.org>, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] perf/arm-smmuv3: Fix lockdep assert in ->event_init()

Thank you for your feedback, Namhyung! Please see my v2 patch:
https://lore.kernel.org/all/20241108050806.3730811-1-ctshao@google.com/

On Thu, Nov 7, 2024 at 5:23 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> On Thu, Nov 07, 2024 at 09:59:20PM +0000, Chun-Tse Shao wrote:
> > Same as
> > https://lore.kernel.org/all/20240514180050.182454-1-namhyung@kernel.org/,
> > we should skip `for_each_sibling_event()` for group leader since it
> > doesn't have the ctx yet.
> >
> > Fixes: f3c0eba28704 ("perf: Add a few assertions")
> > Reported-by: Greg Thelen <gthelen@...gle.com>
> > Cc: Namhyung Kim <namhyung@...nel.org>
> > Cc: Robin Murphy <robin.murphy@....com>
> > Cc: Tuan Phan <tuanphan@...amperecomputing.com>
> > Signed-off-by: Chun-Tse Shao <ctshao@...gle.com>
> > ---
> >  drivers/perf/arm_smmuv3_pmu.c | 7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/perf/arm_smmuv3_pmu.c b/drivers/perf/arm_smmuv3_pmu.c
> > index d5fa92ba8373..09789599fccc 100644
> > --- a/drivers/perf/arm_smmuv3_pmu.c
> > +++ b/drivers/perf/arm_smmuv3_pmu.c
> > @@ -431,6 +431,11 @@ static int smmu_pmu_event_init(struct perf_event *event)
> >                       return -EINVAL;
> >       }
> >
> > +     hwc->idx = -1;
>
> I think you should update the event->cpu as well.
>
> Thanks,
> Namhyung
>
> > +
> > +     if (event->group_leader == event)
> > +             return 0;
> > +
> >       for_each_sibling_event(sibling, event->group_leader) {
> >               if (is_software_event(sibling))
> >                       continue;
> > @@ -442,8 +447,6 @@ static int smmu_pmu_event_init(struct perf_event *event)
> >                       return -EINVAL;
> >       }
> >
> > -     hwc->idx = -1;
> > -
> >       /*
> >        * Ensure all events are on the same cpu so all events are in the
> >        * same cpu context, to avoid races on pmu_enable etc.
> > --
> > 2.47.0.277.g8800431eea-goog
> >