linux-kernel - Re: [PATCH] perf: arm_pmuv3: Fix chained event check for cycle counter

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Message-ID: <20240802102401.GA6004@willie-the-truck>
Date: Fri, 2 Aug 2024 11:24:02 +0100
From: Will Deacon <will@...nel.org>
To: Rob Herring <robh@...nel.org>
Cc: catalin.marinas@....com, Mark Rutland <mark.rutland@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf: arm_pmuv3: Fix chained event check for cycle
 counter

On Thu, Aug 01, 2024 at 11:19:26AM -0600, Rob Herring wrote:
> On Thu, Aug 1, 2024 at 5:29 AM Will Deacon <will@...nel.org> wrote:
> >
> > On Wed, Jul 10, 2024 at 12:23:56PM -0600, Rob Herring (Arm) wrote:
> > > Since commit b7e89b0f5bd7 ("perf: arm_pmu: Remove event index to
> > > counter remapping"), armv8pmu_event_is_chained() is incorrectly
> > > returning that the cycle counter is chained, but the cycle counter has
> > > always been 64-bit. The result is trying to configure counter #30 which
> > > typically doesn't exist.
> > >
> > > As ARMV8_PMU_MAX_GENERAL_COUNTERS is the number of counters (31), the
> > > comparison to the counter index needs to be '<' rather than '<='.
> > >
> > > Fixes: b7e89b0f5bd7 ("perf: arm_pmu: Remove event index to counter remapping")
> > > Signed-off-by: Rob Herring (Arm) <robh@...nel.org>
> > > ---
> > >  drivers/perf/arm_pmuv3.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/perf/arm_pmuv3.c b/drivers/perf/arm_pmuv3.c
> > > index 3b3a3334cc3f..0e22c68fb804 100644
> > > --- a/drivers/perf/arm_pmuv3.c
> > > +++ b/drivers/perf/arm_pmuv3.c
> > > @@ -482,7 +482,7 @@ static bool armv8pmu_event_is_chained(struct perf_event *event)
> > >       return !armv8pmu_event_has_user_read(event) &&
> > >              armv8pmu_event_is_64bit(event) &&
> > >              !armv8pmu_has_long_event(cpu_pmu) &&
> > > -            (idx <= ARMV8_PMU_MAX_GENERAL_COUNTERS);
> > > +            (idx < ARMV8_PMU_MAX_GENERAL_COUNTERS);
> > >  }
> >
> > Acked-by: Will Deacon <will@...nel.org>
> >
> > Catalin -- please can you pick this up as a fix?
> 
> No, this is the fix for what Will dropped and said to resend on the
> v9.4 fixed instruction counter series. Here's the series with the fix
> in it[1].

Urgh, sorry about that, and thanks for pointing it out.

I'd initially marked this as read, but then I was pointed at it the
other day and thought I'd missed a fix since "git show b7e89b0f5bd7"
still shows the patch, despite pruning the remotes.

I'll queue up the other series for 6.12.

Will