linux-kernel - Re: [PATCH] arm_pmu: Invert fallback armpmu_filter() return value (*6.2 regression*)

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Date:   Thu, 16 Feb 2023 14:29:33 +0900
From:   Asahi Lina <lina@...hilina.net>
To:     Janne Grunau <j@...nau.net>, Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ravi Bangoria <ravi.bangoria@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        asahi@...ts.linux.dev
Subject: Re: [PATCH] arm_pmu: Invert fallback armpmu_filter() return value
 (*6.2 regression*)

On 15/02/2023 20.27, Janne Grunau wrote:
> Fixes a regression in "perf: Rewrite core context handling" for arm_pmu
> based drivers without a filter function pointer as the Apple M1 PMU.
> The event is ignored if filter() returns 'true' opposite to
> filter_match(). The refactoring failed to invert the return value if
> arm_pmu has no filter() function pointer of its own.
> 
> Fixes: bd2756811766 ("perf: Rewrite core context handling")
> Signed-off-by: Janne Grunau <j@...nau.net>
> ---
>  drivers/perf/arm_pmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
> index 9b593f985805..9cb22f36cf66 100644
> --- a/drivers/perf/arm_pmu.c
> +++ b/drivers/perf/arm_pmu.c
> @@ -556,7 +556,7 @@ static bool armpmu_filter(struct pmu *pmu, int cpu)
>  	if (ret && armpmu->filter)
>  		return armpmu->filter(pmu, cpu);
>  
> -	return ret;
> +	return !ret;
>  }
>  
>  static ssize_t cpus_show(struct device *dev,
> 
> ---
> base-commit: ceaa837f96adb69c0df0397937cd74991d5d821a
> change-id: 20230215-arm_pmu_m1_regression-b6dd48d0c792
> 
> Best regards,

Tested-by: Asahi Lina <lina@...hilina.net>

This fixes `perf` being completely broken on 6.2. Adding a note to the
subject, I hope this can get picked up before release...

~~ Lina