linux-kernel - Re: [PATCH V10 00/10] arm64/perf: Enable branch stack sampling

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Date:   Mon, 29 May 2023 10:05:07 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        will@...nel.org, catalin.marinas@....com, mark.rutland@....com
Cc:     Mark Brown <broonie@...nel.org>, James Clark <james.clark@....com>,
        Rob Herring <robh@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Suzuki Poulose <suzuki.poulose@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH V10 00/10] arm64/perf: Enable branch stack sampling



On 5/17/23 07:54, Anshuman Khandual wrote:
> This series enables perf branch stack sampling support on arm64 platform
> via a new arch feature called Branch Record Buffer Extension (BRBE). All
> relevant register definitions could be accessed here.
> 
> https://developer.arm.com/documentation/ddi0601/2021-12/AArch64-Registers
> 
> This series applies on 6.4-rc2.
> 
> Changes in V10:
> 
> - Rebased the series on v6.4-rc2
> - Moved ARMV8 PMUV3 changes inside drivers/perf/arm_pmuv3.c
> - Moved BRBE driver changes inside drivers/perf/arm_brbe.[c|h]
> - Moved the WARN_ON() inside the if condition in armv8pmu_handle_irq()

Hello Will/Mark,

There was a crash reported on V9 (applicable here in V10 as well) because of
accessing event->pmu_ctx->task_ctx_data during a PMU IRQ for per-cpu events,
where it would not have been allocated in the first place. I have proposed a
fix for that on the other thread [1]. Besides, does the series looks good in
the current form ? Unless there are other comments, will respin with the fix
later in the week. Thank you.

[1] https://lore.kernel.org/linux-arm-kernel/d02df808-6d2b-c24b-bc8d-8f4859c0c71b@arm.com/

- Anshuman