libbpf-tools: Fix klockstat to finish with -R

On extremely heavy lock contention, klockstat can be stuck in the loop
in print_stats() since it keeps adding new entries to the stat_map.

Instead of deleting the elements in the loop, process them all and then
delete them at the end.

libbpf-tools/klockstat.c

@@ -526,16 +526,9 @@ static int print_stats(struct ksyms *ksyms, int stack_map, int stat_map)
  warn("Out of memory\n");
  return -1;
  }
- ss->stack_id = stack_id;
- if (env.reset) {
- ret = bpf_map_lookup_and_delete_elem(stat_map,
- &stack_id,
- &ss->ls);
- lookup_key = 0;
- } else {
- ret = bpf_map_lookup_elem(stat_map, &stack_id, &ss->ls);
- lookup_key = stack_id;
- }
+
+ lookup_key = ss->stack_id = stack_id;
+ ret = bpf_map_lookup_elem(stat_map, &stack_id, &ss->ls);
  if (ret) {
  free(ss);
  continue;
@@ -575,8 +568,11 @@ static int print_stats(struct ksyms *ksyms, int stack_map, int stat_map)
  print_hld_stat(ksyms, stats[i], nr_stack_entries);
  }
 
- for (i = 0; i < stat_idx; i++)
+ for (i = 0; i < stat_idx; i++) {
+ if (env.reset)
+ bpf_map_delete_elem(stat_map, &ss->stack_id);
  free(stats[i]);
+ }
  free(stats);
 
  return 0;