[DTrace-devel] [PATCH 5/5] bpf: ensure cpuinfo can handle non-sequential CPU ids

[Eugene Loh]

Reviewed-by: Eugene Loh <eugene.loh at oracle.com>
but data seems like a memory leak and a test would be great (though 
probably impractical).

On 5/1/23 15:53, Kris Van Hees via DTrace-devel wrote:
> The 'cpuinfo' BPF map (a per-cpu map) was populated assuming that CPU
> ids are always strictly sequential, i.e. that no gaps in the numbering
> can occur.  That is not a valid assumption.  We need to populate the
> cpuinfo entries referenced by the cpu_id of each online CPU.
>
> Signed-off-by: Kris Van Hees<kris.van.hees at oracle.com>
> ---
>   libdtrace/dt_bpf.c | 15 +++++++++++++--
>   1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/libdtrace/dt_bpf.c b/libdtrace/dt_bpf.c
> index e19833bd..d0487759 100644
> --- a/libdtrace/dt_bpf.c
> +++ b/libdtrace/dt_bpf.c
> @@ -607,15 +607,26 @@ gmap_create_buffers(dtrace_hdl_t *dtp)
>   static int
>   gmap_create_cpuinfo(dtrace_hdl_t *dtp)
>   {
> -	int		fd;
> +	int		i, fd;
>   	uint32_t	key = 0;
> +	dtrace_conf_t	*conf = &dtp->dt_conf;
> +	size_t		ncpus = conf->max_cpuid + 1;
> +	cpuinfo_t	*data;
> +	cpuinfo_t	*ci;
> +
> +	data = dt_zalloc(dtp, ncpus * sizeof(cpuinfo_t));
> +	if (data == NULL)
> +		return dt_set_errno(dtp, EDT_NOMEM);
> +
> +	for (i = 0, ci = &conf->cpus[0]; i < ncpus; i++, ci++)
> +		memcpy(&data[ci->cpu_id], ci, sizeof(cpuinfo_t));
>   
>   	fd = create_gmap(dtp, "cpuinfo", BPF_MAP_TYPE_PERCPU_ARRAY,
>   			 sizeof(uint32_t), sizeof(cpuinfo_t), 1);
>   	if (fd == -1)
>   		return -1;
>   
> -	if (dt_bpf_map_update(fd, &key, dtp->dt_conf.cpus) == -1)
> +	if (dt_bpf_map_update(fd, &key, data) == -1)
>   		return dt_bpf_error(dtp,
>   				    "cannot update BPF map 'cpuinfo': %s\n",
>   				    strerror(errno));
> -- 2.39.1