linux-kernel - Re: [PATCH net v3 6/7] net/sched: act

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Message-ID: <77q-JcImMG2fuQxj_GMUtYmaFAIuPrYMasj4I3aqIVID-Op24JIShBIPgt9kozLZgN4HvsGCS8Ez16mKq4Wq9juL1IOKydWUJwMwCYgHRMg=@1g4.org>
Date: Mon, 26 Jan 2026 08:53:10 +0000
From: Paul Moses <p@....org>
To: Victor Nogueira <victor@...atatu.com>
Cc: netdev@...r.kernel.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>, Simon Horman <horms@...nel.org>, linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH net v3 6/7] net/sched: act_gate: reject empty schedule list

Should REPLACE with an explicit entry list that yields 0 entries return -EINVAL or should it be treated the same as omitting TCA_GATE_ENTRY_LIST and keeping the old schedule?

thanks,
Paul

On Wednesday, January 21st, 2026 at 3:49 PM, Victor Nogueira <victor@...atatu.com> wrote:

> 
> 
> On 21/01/2026 16:44, Victor Nogueira wrote:
> 
> > On 21/01/2026 10:20, Paul Moses wrote:
> > 
> > > Reject empty schedules (num_entries == 0) so next_entry is always
> > > valid and
> > > RCU readers/timer logic never walk an empty list. taprio enforces the
> > > same
> > > constraint on schedules (sch_taprio.c, commit 09dbdf28f9f9fa).
> > > 
> > > Fixes: a51c328df310 ("net: qos: introduce a gate control flow action")
> > > Signed-off-by: Paul Moses p@....org
> > > Cc: stable@...r.kernel.org
> > > ---
> > > net/sched/act_gate.c | 6 ++++++
> > > 1 file changed, 6 insertions(+)
> > > 
> > > diff --git a/net/sched/act_gate.c b/net/sched/act_gate.c
> > > index 48ff378bb051a..e4134b9a4a314 100644
> > > --- a/net/sched/act_gate.c
> > > +++ b/net/sched/act_gate.c
> > > @@ -509,6 +509,12 @@ static int tcf_gate_init(struct net *net, struct
> > > nlattr *nla,
> > > cycletime_ext = nla_get_u64(tb[TCA_GATE_CYCLE_TIME_EXT]);
> > > p->tcfg_cycletime_ext = cycletime_ext;
> > > + if (p->num_entries == 0) {
> > > + NL_SET_ERR_MSG(extack, "The entry list is empty");
> > > + err = -EINVAL;
> > > + goto release_mem;
> > > + }
> > 
> > It would be simpler to check this in parse_gate_list.
> > That way you could return -EINVAL there directly
> > in case 0 entries were passed.
> 
> 
> On second thought, I believe it would be better
> to check whether parse_gate_list's return is 0
> and the op is a create. Something like:
> 
> err = parse_gate_list(tb[TCA_GATE_ENTRY_LIST], p, extack);
> ...
> if (!err && ret == ACT_P_CREATED) {
> NL_SET_ERR_MSG(extack, "The entry list is empty");
> err = -EINVAL;
> goto release_mem;
> }
> 
> so that you don't need to add new arguments to
> parse_gate_list.
> 
> cheers,
> Victor