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

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

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.
>

Let us run some basic tests on this first - it's a hairy spot. Also,
IIRC Cong had some reservations about this in the past. Can't remember
what they were.

cheers,
jamal


> 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
>