On Mon, 15 Dec 2025 22:13:57 +0100
Jiri Olsa [off-list ref] wrote:

+/**
+ * hash_add - adds two struct ftrace_hash and returns the result
+ * @a: struct ftrace_hash object
+ * @b: struct ftrace_hash object
+ *
+ * Returns struct ftrace_hash object on success, NULL on error.
+ */
+static struct ftrace_hash *hash_add(struct ftrace_hash *a, struct ftrace_hash *b)
+{
+	struct ftrace_func_entry *entry;
+	struct ftrace_hash *add;
+	int size, i;
+
+	size = hash_count(a) + hash_count(b);
+	if (size > 32)
+		size = 32;
+
+	add = alloc_and_copy_ftrace_hash(fls(size), a);
+	if (!add)
+		goto error;

You can just return NULL here, as add is NULL.

+
+	size = 1 << b->size_bits;
+	for (i = 0; i < size; i++) {
+		hlist_for_each_entry(entry, &b->buckets[i], hlist) {
+			if (add_hash_entry_direct(add, entry->ip, entry->direct) == NULL)
+				goto error;

Could remove the error and have:

			if (add_hash_entry_direct(add, entry->ip, entry->direct) == NULL) {
				free_ftrace_hash(add);
				return NULL;
			}

+		}
+	}
+	return add;
+
+ error:
+	free_ftrace_hash(add);
+	return NULL;
+}
+

Non static functions require a kerneldoc header.

+int update_ftrace_direct_add(struct ftrace_ops *ops, struct ftrace_hash *hash)
+{
+	struct ftrace_hash *old_direct_functions = NULL, *new_direct_functions;
+	struct ftrace_hash *old_filter_hash, *new_filter_hash = NULL;

BTW, I prefer to not double up on variables. That is to have each on
their own lines. Makes it easier to read for me.

+	struct ftrace_func_entry *entry;
+	int i, size, err = -EINVAL;

Even here.

+	bool reg;
+
+	if (!hash_count(hash))
+		return -EINVAL;
+
+	mutex_lock(&direct_mutex);
+
+	/* Make sure requested entries are not already registered. */
+	size = 1 << hash->size_bits;
+	for (i = 0; i < size; i++) {

If you want, you can remove the i declaration and use for(int i = 0; ... here.

+		hlist_for_each_entry(entry, &hash->buckets[i], hlist) {
+			if (__ftrace_lookup_ip(direct_functions, entry->ip))
+				goto out_unlock;
+		}
+	}
+
+	old_filter_hash = ops->func_hash ? ops->func_hash->filter_hash : NULL;
+
+	/* If there's nothing in filter_hash we need to register the ops. */
+	reg = hash_count(old_filter_hash) == 0;
+	if (reg) {
+		if (ops->func || ops->trampoline)
+			goto out_unlock;
+		if (ops->flags & FTRACE_OPS_FL_ENABLED)
+			goto out_unlock;
+	}
+
+	err = -ENOMEM;
+	new_filter_hash = hash_add(old_filter_hash, hash);
+	if (!new_filter_hash)
+		goto out_unlock;
+
+	new_direct_functions = hash_add(direct_functions, hash);
+	if (!new_direct_functions)
+		goto out_unlock;
+
+	old_direct_functions = direct_functions;
+	rcu_assign_pointer(direct_functions, new_direct_functions);
+
+	if (reg) {
+		ops->func = call_direct_funcs;
+		ops->flags |= MULTI_FLAGS;
+		ops->trampoline = FTRACE_REGS_ADDR;
+		ops->local_hash.filter_hash = new_filter_hash;
+
+		err = register_ftrace_function_nolock(ops);
+		if (err) {
+			/* restore old filter on error */
+			ops->local_hash.filter_hash = old_filter_hash;
+
+			/* cleanup for possible another register call */
+			ops->func = NULL;
+			ops->trampoline = 0;
+		} else {
+			new_filter_hash = old_filter_hash;
+		}
+	} else {
+		err = ftrace_update_ops(ops, new_filter_hash, EMPTY_HASH);
+		/*
+		 * new_filter_hash is dup-ed, so we need to release it anyway,
+		 * old_filter_hash either stays on error or is already released
+		 */
+	}
+
+	if (err) {
+		/* reset direct_functions and free the new one */
+		rcu_assign_pointer(direct_functions, old_direct_functions);
+		old_direct_functions = new_direct_functions;
+	}
+
+ out_unlock:
+	mutex_unlock(&direct_mutex);
+
+	if (old_direct_functions && old_direct_functions != EMPTY_HASH)
+		call_rcu_tasks(&old_direct_functions->rcu, register_ftrace_direct_cb);
+	if (new_filter_hash)

free_ftrace_hash() checks for NULL, so you don't need the above if statement.

+		free_ftrace_hash(new_filter_hash);
+
+	return err;

-- Steve

+}
+
 #endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */
 
 /**