libbpf: remove unnecessary struct_ops prog validity check

libbpf ensures that BPF program references set in map->st_ops->progs[i]
during open phase are always valid STRUCT_OPS programs. This is done in
bpf_object__collect_st_ops_relos(). So there is no need to double-check
that in bpf_map__init_kern_struct_ops().

Simplify the code by removing unnecessary check. Also, we avoid using
local prog variable to keep code similar to the upcoming fix, which adds
similar logic in another part of bpf_map__init_kern_struct_ops().
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20240507001335.1445325-2-andrii@kernel.orgSigned-off-by: Martin KaFai Lau <martin.lau@kernel.org>

tools/lib/bpf/libbpf.c

@@ -1152,22 +1152,15 @@ static int bpf_map__init_kern_struct_ops(struct bpf_map *map)
 				return -ENOTSUP;
 			}
 
-			prog = st_ops->progs[i];
-			if (prog) {
+			if (st_ops->progs[i]) {
 				/* If we had declaratively set struct_ops callback, we need to
-				 * first validate that it's actually a struct_ops program.
-				 * And then force its autoload to false, because it doesn't have
+				 * force its autoload to false, because it doesn't have
 				 * a chance of succeeding from POV of the current struct_ops map.
 				 * If this program is still referenced somewhere else, though,
 				 * then bpf_object_adjust_struct_ops_autoload() will update its
 				 * autoload accordingly.
 				 */
-				if (!is_valid_st_ops_program(obj, prog)) {
-					pr_warn("struct_ops init_kern %s: member %s is declaratively assigned a non-struct_ops program\n",
-						map->name, mname);
-					return -EINVAL;
-				}
-				prog->autoload = false;
+				st_ops->progs[i]->autoload = false;
 				st_ops->progs[i] = NULL;
 			}