Re: [PATCHv5 bpf-next 5/9] ftrace: Add update_ftrace_direct_del function

Steven Rostedt
2025-12-18T01:48:17Z

On Mon, 15 Dec 2025 22:13:58 +0100
Jiri Olsa <jolsa@kernel.org> 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 */
>
> /**