linux-kernel - Re: [PATCHv5 bpf-next 5/9] ftrace: Add update_ftrace_direct

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Message-ID: <aUUakb_Bv1sDfJUR@krava>
Date: Fri, 19 Dec 2025 10:27:45 +0100
From: Jiri Olsa <olsajiri@...il.com>
To: Steven Rostedt <rostedt@...nel.org>
Cc: Florent Revest <revest@...gle.com>, Mark Rutland <mark.rutland@....com>,
	bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Menglong Dong <menglong8.dong@...il.com>,
	Song Liu <song@...nel.org>
Subject: Re: [PATCHv5 bpf-next 5/9] ftrace: Add update_ftrace_direct_del
 function

On Wed, Dec 17, 2025 at 08:48:14PM -0500, Steven Rostedt wrote:
> On Mon, 15 Dec 2025 22:13:58 +0100
> Jiri Olsa <jolsa@...nel.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;

ok

> 
> > +
> > +	size = 1 << b->size_bits;
> > +	for (i = 0; i < size; i++) {
> 
> You can make this for (int i = 0; ...) too.

ok

> 
> > +		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:

ok

> 
> 			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.

ok

> 
> > +	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; ...) 

ack

thanks,
jirka