Re: [PATCH] perf: fix segfault in `lock contention -b`

[K Prateek Nayak]

Hello Tycho,

On 1/9/2026 10:14 PM, Tycho Andersen wrote:
> @@ -43,19 +43,20 @@ static void check_slab_cache_iter(struct lock_contention *con)
>  	con->btf = btf__load_vmlinux_btf();
>  	if (con->btf == NULL) {
>  		pr_debug("BTF loading failed: %s\n", strerror(errno));
> -		return;
> +		return -errno;
>  	}
>  
>  	ret = btf__find_by_name_kind(con->btf, "bpf_iter__kmem_cache", BTF_KIND_STRUCT);
>  	if (ret < 0) {
>  		bpf_program__set_autoload(skel->progs.slab_cache_iter, false);
>  		pr_debug("slab cache iterator is not available: %d\n", ret);
> -		return;
> +		return ret;
>  	}
>  
>  	has_slab_iter = true;
>  
>  	bpf_map__set_max_entries(skel->maps.slab_caches, con->map_nr_entries);
> +	return 0;
>  }
>  
>  static void run_slab_cache_iter(void)
> @@ -301,7 +302,8 @@ int lock_contention_prepare(struct lock_contention *con)
>  			skel->rodata->use_cgroup_v2 = 1;
>  	}
>  
> -	check_slab_cache_iter(con);
> +	if (check_slab_cache_iter(con) < 0)
> +		return -1;
>  
>  	if (con->filters->nr_slabs && has_slab_iter) {

nit.

Now that lock_contention_prepare() bails out when
check_slab_cache_iter() fails, we no longer need the "has_slab_iter"
global indicator.

Both this, and run_slab_cache_iter() that depend on "has_slab_iter"
will only run if check_slab_cache_iter() succeeded and the global
indicator will be true in both those cases.

Can be separate follow-up cleanup.

>  		skel->rodata->has_slab = 1;
> 
> base-commit: 5572ad8fddecd4a0db19801262072ff5916b7589

-- 
Thanks and Regards,
Prateek