linux-kernel - Re: [PATCH net-next v2 2/9] net: sched: act

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Date: Tue, 18 Jun 2024 07:38:47 +0000
From: Adrián Moreno <amorenoz@...hat.com>
To: Ilya Maximets <i.maximets@....org>
Cc: netdev@...r.kernel.org, aconole@...hat.com, echaudro@...hat.com, 
	horms@...nel.org, dev@...nvswitch.org, Jamal Hadi Salim <jhs@...atatu.com>, 
	Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v2 2/9] net: sched: act_sample: add action cookie
 to sample

On Mon, Jun 17, 2024 at 12:00:04PM GMT, Ilya Maximets wrote:
> On 6/3/24 20:56, Adrian Moreno wrote:
> > If the action has a user_cookie, pass it along to the sample so it can
> > be easily identified.
> >
> > Signed-off-by: Adrian Moreno <amorenoz@...hat.com>
> > ---
> >  net/sched/act_sample.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> >
> > diff --git a/net/sched/act_sample.c b/net/sched/act_sample.c
> > index a69b53d54039..5c3f86ec964a 100644
> > --- a/net/sched/act_sample.c
> > +++ b/net/sched/act_sample.c
> > @@ -165,9 +165,11 @@ TC_INDIRECT_SCOPE int tcf_sample_act(struct sk_buff *skb,
> >  				     const struct tc_action *a,
> >  				     struct tcf_result *res)
> >  {
> > +	u8 cookie_data[TC_COOKIE_MAX_SIZE] = {};
>
> Is it necessary to initialize these 16 bytes on every call?
> Might be expensive.  We're passing the data length around,
> so the uninitialized parts should not be accessed.
>

They "should" not, indeed. I was just trying to be extra careful.
Are you worried TC_COOKIE_MAX_SIZE could grow or the cycles needed to
clear the current 16 bytes?

> Best regards, Ilya Maximets.
>
> >  	struct tcf_sample *s = to_sample(a);
> >  	struct psample_group *psample_group;
> >  	struct psample_metadata md = {};
> > +	struct tc_cookie *user_cookie;
> >  	int retval;
> >
> >  	tcf_lastuse_update(&s->tcf_tm);
> > @@ -189,6 +191,16 @@ TC_INDIRECT_SCOPE int tcf_sample_act(struct sk_buff *skb,
> >  		if (skb_at_tc_ingress(skb) && tcf_sample_dev_ok_push(skb->dev))
> >  			skb_push(skb, skb->mac_len);
> >
> > +		rcu_read_lock();
> > +		user_cookie = rcu_dereference(a->user_cookie);
> > +		if (user_cookie) {
> > +			memcpy(cookie_data, user_cookie->data,
> > +			       user_cookie->len);
> > +			md.user_cookie = cookie_data;
> > +			md.user_cookie_len = user_cookie->len;
> > +		}
> > +		rcu_read_unlock();
> > +
> >  		md.trunc_size = s->truncate ? s->trunc_size : skb->len;
> >  		psample_sample_packet(psample_group, skb, s->rate, &md);
> >
>