Re: [PATCH net] net/sched: act_mirred: use the backlog for mirred ingress

[Jamal Hadi Salim <jhs@mojatatu.com>]

On Wed, Feb 14, 2024 at 10:11 AM Jamal Hadi Salim <jhs@mojatatu.com> wrote:
>
> On Fri, Feb 9, 2024 at 6:54 PM Jakub Kicinski <kuba@kernel.org> wrote:
> >
> > The test Davide added in commit ca22da2fbd69 ("act_mirred: use the backlog
> > for nested calls to mirred ingress") hangs our testing VMs every 10 or so
> > runs, with the familiar tcp_v4_rcv -> tcp_v4_rcv deadlock reported by
> > lockdep.
> >
> > In the past there was a concern that the backlog indirection will
> > lead to loss of error reporting / less accurate stats. But the current
> > workaround does not seem to address the issue.
> >
> > Fixes: 53592b364001 ("net/sched: act_mirred: Implement ingress actions")
> > Cc: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
> > Suggested-by: Davide Caratti <dcaratti@redhat.com>
> > Link: https://lore.kernel.org/netdev/33dc43f587ec1388ba456b4915c75f02a8aae226.1663945716.git.dcaratti@redhat.com/
> > Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> > ---
> > CC: jhs@mojatatu.com
> > CC: xiyou.wangcong@gmail.com
> > CC: jiri@resnulli.us
> > CC: shmulik.ladkani@gmail.com
> > ---
> >  net/sched/act_mirred.c                             | 14 +++++---------
> >  .../testing/selftests/net/forwarding/tc_actions.sh |  3 ---
> >  2 files changed, 5 insertions(+), 12 deletions(-)
> >
> > diff --git a/net/sched/act_mirred.c b/net/sched/act_mirred.c
> > index 93a96e9d8d90..35c366f043d9 100644
> > --- a/net/sched/act_mirred.c
> > +++ b/net/sched/act_mirred.c
> > @@ -232,18 +232,14 @@ static int tcf_mirred_init(struct net *net, struct nlattr *nla,
> >         return err;
> >  }
> >
> > -static bool is_mirred_nested(void)
> > -{
> > -       return unlikely(__this_cpu_read(mirred_nest_level) > 1);
> > -}
> > -
> > -static int tcf_mirred_forward(bool want_ingress, struct sk_buff *skb)
> > +static int
> > +tcf_mirred_forward(bool at_ingress, bool want_ingress, struct sk_buff *skb)
> >  {
> >         int err;
> >
> >         if (!want_ingress)
> >                 err = tcf_dev_queue_xmit(skb, dev_queue_xmit);
> > -       else if (is_mirred_nested())
> > +       else if (!at_ingress)
> >                 err = netif_rx(skb);
> >         else
> >                 err = netif_receive_skb(skb);
> > @@ -319,9 +315,9 @@ static int tcf_mirred_to_dev(struct sk_buff *skb, struct tcf_mirred *m,
> >
> >                 skb_set_redirected(skb_to_send, skb_to_send->tc_at_ingress);
> >
> > -               err = tcf_mirred_forward(want_ingress, skb_to_send);
> > +               err = tcf_mirred_forward(at_ingress, want_ingress, skb_to_send);
> >         } else {
> > -               err = tcf_mirred_forward(want_ingress, skb_to_send);
> > +               err = tcf_mirred_forward(at_ingress, want_ingress, skb_to_send);
> >         }
> >
> >         if (err) {
> > diff --git a/tools/testing/selftests/net/forwarding/tc_actions.sh b/tools/testing/selftests/net/forwarding/tc_actions.sh
> > index b0f5e55d2d0b..589629636502 100755
> > --- a/tools/testing/selftests/net/forwarding/tc_actions.sh
> > +++ b/tools/testing/selftests/net/forwarding/tc_actions.sh
> > @@ -235,9 +235,6 @@ mirred_egress_to_ingress_tcp_test()
> >         check_err $? "didn't mirred redirect ICMP"
> >         tc_check_packets "dev $h1 ingress" 102 10
> >         check_err $? "didn't drop mirred ICMP"
> > -       local overlimits=$(tc_rule_stats_get ${h1} 101 egress .overlimits)
> > -       test ${overlimits} = 10
> > -       check_err $? "wrong overlimits, expected 10 got ${overlimits}"
> >
> >         tc filter del dev $h1 egress protocol ip pref 100 handle 100 flower
> >         tc filter del dev $h1 egress protocol ip pref 101 handle 101 flower
> > --
> > 2.43.0
> >
>
>
> Doing a quick test of this and other patch i saw..


So tests pass - but on the list i only see one patch and the other is
on lore, not sure how to ACK something that is not on email, but FWIW:
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>

The second patch avoids the recursion issue (which was the root cause)
and the first patch is really undoing ca22da2fbd693
I dont know underlying issue in ca22da2fbd693 is solved (and dont have
time to look into it). Davide?

cheers,
jamal

> cheers,
> jamal