Re: [PATCH v1 1/4] perf off-cpu: Use the CPU map index for the bpf-output file descriptor

[James Clark]

On 27/10/2026 17:04, Ian Rogers wrote:
> When populating the offcpu_output BPF perf event array, the file
> descriptor of the bpf-output event was looked up using the CPU number
> rather than the index within the evsel's CPU map. These differ when
> CPUs are offline or a subset of CPUs is used, leading to the wrong, or
> an out-of-bounds, file descriptor being used. Index the file
> descriptor array using the CPU map index.
>
> Fixes: 282c195906c7 ("perf record --off-cpu: Preparation of off-cpu BPF program")
> Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> ---
>   tools/perf/util/bpf_off_cpu.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/bpf_off_cpu.c b/tools/perf/util/bpf_off_cpu.c
> index c4639f6a5776..ff8935688b43 100644
> --- a/tools/perf/util/bpf_off_cpu.c
> +++ b/tools/perf/util/bpf_off_cpu.c
> @@ -95,7 +95,7 @@ static void off_cpu_start(void *arg)
>   		int cpu_nr = pcpu.cpu;
>   
>   		err = bpf_map__update_elem(skel->maps.offcpu_output, &cpu_nr, sizeof(int),
> -					   xyarray__entry(evsel->core.fd, cpu_nr, 0),
> +					   xyarray__entry(evsel->core.fd, i, 0),
>   					   sizeof(int), BPF_ANY);
>   		if (err) {
>   			pr_err("Failed to update perf event map for direct off-cpu dumping\n");


Reviewed-by: James Clark <james.clark@xxxxxxxxxx>