Re: [PATCHv5 bpf-next 4/9] ftrace: Add update_ftrace_direct_add function

Jiri Olsa
2025-12-19T09:27:42Z

On Wed, Dec 17, 2025 at 08:39:09PM -0500, Steven Rostedt wrote:
> On Mon, 15 Dec 2025 22:13:57 +0100
> Jiri Olsa <jolsa@kernel.org> 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.

ok

>
> > +
> > + 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;
> }

ok

>
>
> > + }
> > + }
> > + return add;
> > +
> > + error:
> > + free_ftrace_hash(add);
> > + return NULL;
> > +}
> > +
>
> Non static functions require a kerneldoc header.

ah right, will add

>
> > +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.

ok, will split

>
> > + 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.

ok

SNIP

> > + }
> > +
> > + 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.

ok

thanks,
jirka