On Mon, 15 Dec 2025 22:13:58 +0100
Jiri Olsa [off-list ref] wrote:

+/**
+ * hash_sub - substracts @b from @a 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_sub(struct ftrace_hash *a, struct ftrace_hash *b)
+{
+	struct ftrace_func_entry *entry, *del;
+	struct ftrace_hash *sub;
+	int size, i;
+
+	sub = alloc_and_copy_ftrace_hash(a->size_bits, a);
+	if (!sub)
+		goto error;

Again, this can be just return NULL;

+
+	size = 1 << b->size_bits;
+	for (i = 0; i < size; i++) {

You can make this for (int i = 0; ...) too.

+		hlist_for_each_entry(entry, &b->buckets[i], hlist) {
+			del = __ftrace_lookup_ip(sub, entry->ip);
+			if (WARN_ON_ONCE(!del))
+				goto error;

And you can remove the error label here too:

			if (WARN_ON_ONCE(!del)) {
				free_ftrace_hash(sub);
				return NULL;
			}

+			remove_hash_entry(sub, del);
+			kfree(del);
+		}
+	}
+	return sub;
+
+ error:
+	free_ftrace_hash(sub);
+	return NULL;
+}
+
+int update_ftrace_direct_del(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;
+	struct ftrace_func_entry *del, *entry;

One variable per line.

+	unsigned long size, i;
+	int err = -EINVAL;
+
+	if (!hash_count(hash))
+		return -EINVAL;
+	if (check_direct_multi(ops))
+		return -EINVAL;
+	if (!(ops->flags & FTRACE_OPS_FL_ENABLED))
+		return -EINVAL;
+	if (direct_functions == EMPTY_HASH)
+		return -EINVAL;
+
+	mutex_lock(&direct_mutex);
+
+	old_filter_hash = ops->func_hash ? ops->func_hash->filter_hash : NULL;
+
+	if (!hash_count(old_filter_hash))
+		goto out_unlock;
+
+	/* Make sure requested entries are already registered. */
+	size = 1 << hash->size_bits;
+	for (i = 0; i < size; i++) {

	for (int i = 0; ...) 

-- Steve

+		hlist_for_each_entry(entry, &hash->buckets[i], hlist) {
+			del = __ftrace_lookup_ip(direct_functions, entry->ip);
+			if (!del || del->direct != entry->direct)
+				goto out_unlock;
+		}
+	}
+
+	err = -ENOMEM;
+	new_filter_hash = hash_sub(old_filter_hash, hash);
+	if (!new_filter_hash)
+		goto out_unlock;
+
+	new_direct_functions = hash_sub(direct_functions, hash);
+	if (!new_direct_functions)
+		goto out_unlock;
+
+	/* If there's nothing left, we need to unregister the ops. */
+	if (ftrace_hash_empty(new_filter_hash)) {
+		err = unregister_ftrace_function(ops);
+		if (!err) {
+			/* cleanup for possible another register call */
+			ops->func = NULL;
+			ops->trampoline = 0;
+			ftrace_free_filter(ops);
+			ops->func_hash->filter_hash = NULL;
+		}
+	} 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) {
+		/* free the new_direct_functions */
+		old_direct_functions = new_direct_functions;
+	} else {
+		rcu_assign_pointer(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);
+	free_ftrace_hash(new_filter_hash);
+
+	return err;
+}
+
 #endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */
 
 /**