drivers: perf: Fix wrong put_cpu() placement

[PATCH -fixes] drivers: perf: Fix wrong put_cpu() placement

Posted by Alexandre Ghiti 1 week, 4 days ago

Unfortunately, the wrong patch version was merged which places the
put_cpu() after enabling a static key, which is not safe as pointed by
Will [1], so move put_cpu() before to avoid this.

Fixes: 2840dadf0dde ("drivers: perf: Fix smp_processor_id() use in preemptible code")
Reported-by: Atish Patra <atishp@rivosinc.com>
Link: https://lore.kernel.org/all/20240827125335.GD4772@willie-the-truck/ [1]
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
---
 drivers/perf/riscv_pmu_sbi.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
index 391ca1422cae..1aa303f76cc7 100644
--- a/drivers/perf/riscv_pmu_sbi.c
+++ b/drivers/perf/riscv_pmu_sbi.c
@@ -1393,8 +1393,9 @@ static int pmu_sbi_device_probe(struct platform_device *pdev)
 			goto out_unregister;
 
 		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);
@@ -1408,7 +1409,6 @@ 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

Re: [PATCH -fixes] drivers: perf: Fix wrong put_cpu() placement

Posted by Atish Kumar Patra 1 week, 3 days ago

On Tue, Nov 12, 2024 at 3:34 AM Alexandre Ghiti <alexghiti@rivosinc.com> wrote:
>
> Unfortunately, the wrong patch version was merged which places the
> put_cpu() after enabling a static key, which is not safe as pointed by
> Will [1], so move put_cpu() before to avoid this.
>
> Fixes: 2840dadf0dde ("drivers: perf: Fix smp_processor_id() use in preemptible code")
> Reported-by: Atish Patra <atishp@rivosinc.com>
> Link: https://lore.kernel.org/all/20240827125335.GD4772@willie-the-truck/ [1]
> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
> ---
>  drivers/perf/riscv_pmu_sbi.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
> index 391ca1422cae..1aa303f76cc7 100644
> --- a/drivers/perf/riscv_pmu_sbi.c
> +++ b/drivers/perf/riscv_pmu_sbi.c
> @@ -1393,8 +1393,9 @@ static int pmu_sbi_device_probe(struct platform_device *pdev)
>                         goto out_unregister;
>
>                 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);
> @@ -1408,7 +1409,6 @@ 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
>

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