linux-kernel - Re: [PATCH -fixes v2] drivers: perf: Fix smp_processor

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Message-ID: <6d20b21d-7e88-4072-b33d-dbb45d2f0965@rivosinc.com>
Date: Fri, 30 Aug 2024 09:39:52 -0700
From: Atish Patra <atishp@...osinc.com>
To: Alexandre Ghiti <alexghiti@...osinc.com>,
 Atish Patra <atishp@...shpatra.org>, Anup Patel <anup@...infault.org>,
 Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>,
 Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt
 <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 linux-riscv@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Cc: Andrea Parri <parri.andrea@...il.com>, Nam Cao <namcao@...utronix.de>
Subject: Re: [PATCH -fixes v2] drivers: perf: Fix smp_processor_id() use in
 preemptible code

On 8/29/24 2:00 AM, Alexandre Ghiti wrote:
> As reported in [1], the use of smp_processor_id() in
> pmu_sbi_device_probe() must be protected by disabling the preemption, so
> simply use get_cpu()/put_cpu() instead.
> 
> Reported-by: Andrea Parri <parri.andrea@...il.com>
> Reported-by: Nam Cao <namcao@...utronix.de>
> Closes: https://lore.kernel.org/linux-riscv/20240820074925.ReMKUPP3@linutronix.de/ [1]
> Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>
> ---
> 
> Changes in v2:
> - Do not disable the preemption in static_key_enable() (Will)
> 
>   drivers/perf/riscv_pmu_sbi.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
> index 31a17a56eb3b..febd8e74a72f 100644
> --- a/drivers/perf/riscv_pmu_sbi.c
> +++ b/drivers/perf/riscv_pmu_sbi.c
> @@ -1373,11 +1373,16 @@ static int pmu_sbi_device_probe(struct platform_device *pdev)
>   
>   	/* SBI PMU Snapsphot is only available in SBI v2.0 */
>   	if (sbi_v2_available) {
> +		int cpu;
> +
>   		ret = pmu_sbi_snapshot_alloc(pmu);
>   		if (ret)
>   			goto out_unregister;
>   
> -		ret = pmu_sbi_snapshot_setup(pmu, smp_processor_id());
> +		cpu = get_cpu();
> +		ret = pmu_sbi_snapshot_setup(pmu, cpu);
> +		put_cpu();
> +
>   		if (ret) {
>   			/* Snapshot is an optional feature. Continue if not available */
>   			pmu_sbi_snapshot_free(pmu);

Reviewed-by: Atish Patra <atishp@...osinc.com>