[PATCH -fixes] drivers: perf: Fix smp_processor_id() use in preemptible code

[Anup Patel]

On Mon, Aug 26, 2024 at 10:22 PM Alexandre Ghiti <alexghiti at rivosinc.com> wrote:
>
> As reported in [1], the use of smp_processor_id() in
> pmu_sbi_device_probe() must be protected by disabling the preemption, so
> simple use get_cpu()/put_cpu() instead.
>
> Reported-by: Nam Cao <namcao at linutronix.de>
> Closes: https://lore.kernel.org/linux-riscv/20240820074925.ReMKUPP3@linutronix.de/ [1]
> Signed-off-by: Alexandre Ghiti <alexghiti at rivosinc.com>

LGTM.

Reviewed-by: Anup Patel <anup at brainfault.org>

Regards,
Anup

> ---
>  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..25b1b699b3e2 100644
> --- a/drivers/perf/riscv_pmu_sbi.c
> +++ b/drivers/perf/riscv_pmu_sbi.c
> @@ -1373,11 +1373,15 @@ 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);
>                 if (ret) {
>                         /* Snapshot is an optional feature. Continue if not available */
>                         pmu_sbi_snapshot_free(pmu);
> @@ -1391,6 +1395,7 @@ static int pmu_sbi_device_probe(struct platform_device *pdev)
>                          */
>                         static_branch_enable(&sbi_pmu_snapshot_available);
>                 }
> +               put_cpu();
>         }
>
>         register_sysctl("kernel", sbi_pmu_sysctl_table);
> --
> 2.39.2
>