linux-kernel - Re: [PATCH] perf/arm-dmc620: Fix lockdep assert in ->event

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Message-ID: <20240517120234.GA32598@willie-the-truck>
Date: Fri, 17 May 2024 13:02:34 +0100
From: Will Deacon <will@...nel.org>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Mark Rutland <mark.rutland@....com>, Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-arm-kernel@...ts.infradead.org,
	Greg Thelen <gthelen@...gle.com>,
	Robin Murphy <robin.murphy@....com>,
	Tuan Phan <tuanphan@...amperecomputing.com>
Subject: Re: [PATCH] perf/arm-dmc620: Fix lockdep assert in ->event_init()

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@...gle.com>
> Cc: Robin Murphy <robin.murphy@....com>
> Cc: Tuan Phan <tuanphan@...amperecomputing.com>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  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;
>  
>  	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