[PATCH nf] sched: act_ct: additional checks for outdated flows

[PATCH nf] sched: act_ct: additional checks for outdated flows

[Pablo Neira Ayuso]

From: Vlad Buslov <vladbu@nvidia.com>

Current nf_flow_is_outdated() implementation considers any flow table flow
which state diverged from its underlying CT connection status for teardown
which can be problematic in the following cases:

- Flow has never been offloaded to hardware in the first place either
because flow table has hardware offload disabled (flag
NF_FLOWTABLE_HW_OFFLOAD is not set) or because it is still pending on 'add'
workqueue to be offloaded for the first time. The former is incorrect, the
later generates excessive deletions and additions of flows.

- Flow is already pending to be updated on the workqueue. Tearing down such
flows will also generate excessive removals from the flow table, especially
on highly loaded system where the latency to re-offload a flow via 'add'
workqueue can be quite high.

When considering a flow for teardown as outdated verify that it is both
offloaded to hardware and doesn't have any pending updates.

Fixes: 41f2c7c342d3 ("net/sched: act_ct: Fix promotion of offloaded unreplied tuple")
Reviewed-by: Paul Blakey <paulb@nvidia.com>
Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
I am taking Vlad's patch and rebasing as per his request:

This patch requires:
https://patchwork.ozlabs.org/project/netfilter-devel/patch/20231024193815.1987-1-pablo@netfilter.org/

 net/sched/act_ct.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/sched/act_ct.c b/net/sched/act_ct.c
index 0d44da4e8c8e..fb52d6f9aff9 100644
--- a/net/sched/act_ct.c
+++ b/net/sched/act_ct.c
@@ -281,6 +281,8 @@ static int tcf_ct_flow_table_fill_actions(struct net *net,
 static bool tcf_ct_flow_is_outdated(const struct flow_offload *flow)
 {
 	return test_bit(IPS_SEEN_REPLY_BIT, &flow->ct->status) &&
+	       test_bit(IPS_HW_OFFLOAD_BIT, &flow->ct->status) &&
+	       !test_bit(NF_FLOW_HW_PENDING, &flow->flags) &&
 	       !test_bit(NF_FLOW_HW_ESTABLISHED, &flow->flags);
 }
 
-- 
2.30.2

Re: [PATCH nf] sched: act_ct: additional checks for outdated flows

[Vlad Buslov]

On Tue 24 Oct 2023 at 22:02, Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> From: Vlad Buslov <vladbu@nvidia.com>
>
> Current nf_flow_is_outdated() implementation considers any flow table flow
> which state diverged from its underlying CT connection status for teardown
> which can be problematic in the following cases:
>
> - Flow has never been offloaded to hardware in the first place either
> because flow table has hardware offload disabled (flag
> NF_FLOWTABLE_HW_OFFLOAD is not set) or because it is still pending on 'add'
> workqueue to be offloaded for the first time. The former is incorrect, the
> later generates excessive deletions and additions of flows.
>
> - Flow is already pending to be updated on the workqueue. Tearing down such
> flows will also generate excessive removals from the flow table, especially
> on highly loaded system where the latency to re-offload a flow via 'add'
> workqueue can be quite high.
>
> When considering a flow for teardown as outdated verify that it is both
> offloaded to hardware and doesn't have any pending updates.
>
> Fixes: 41f2c7c342d3 ("net/sched: act_ct: Fix promotion of offloaded unreplied tuple")
> Reviewed-by: Paul Blakey <paulb@nvidia.com>
> Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
> ---
> I am taking Vlad's patch and rebasing as per his request:
>
> This patch requires:
> https://patchwork.ozlabs.org/project/netfilter-devel/patch/20231024193815.1987-1-pablo@netfilter.org/
>

Signed-off-by: Vlad Buslov <vladbu@nvidia.com>

Re: [PATCH nf] sched: act_ct: additional checks for outdated flows

[Paul Blakey]

On 24/10/2023 23:02, Pablo Neira Ayuso wrote:
> From: Vlad Buslov <vladbu@nvidia.com>
> 
> Current nf_flow_is_outdated() implementation considers any flow table flow
> which state diverged from its underlying CT connection status for teardown
> which can be problematic in the following cases:
> 
> - Flow has never been offloaded to hardware in the first place either
> because flow table has hardware offload disabled (flag
> NF_FLOWTABLE_HW_OFFLOAD is not set) or because it is still pending on 'add'
> workqueue to be offloaded for the first time. The former is incorrect, the
> later generates excessive deletions and additions of flows.
> 
> - Flow is already pending to be updated on the workqueue. Tearing down such
> flows will also generate excessive removals from the flow table, especially
> on highly loaded system where the latency to re-offload a flow via 'add'
> workqueue can be quite high.
> 
> When considering a flow for teardown as outdated verify that it is both
> offloaded to hardware and doesn't have any pending updates.
> 
> Fixes: 41f2c7c342d3 ("net/sched: act_ct: Fix promotion of offloaded unreplied tuple")
> Reviewed-by: Paul Blakey <paulb@nvidia.com>
> Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
> ---
> I am taking Vlad's patch and rebasing as per his request:
> 
> This patch requires:
> https://patchwork.ozlabs.org/project/netfilter-devel/patch/20231024193815.1987-1-pablo@netfilter.org/
> 
>   net/sched/act_ct.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/net/sched/act_ct.c b/net/sched/act_ct.c
> index 0d44da4e8c8e..fb52d6f9aff9 100644
> --- a/net/sched/act_ct.c
> +++ b/net/sched/act_ct.c
> @@ -281,6 +281,8 @@ static int tcf_ct_flow_table_fill_actions(struct net *net,
>   static bool tcf_ct_flow_is_outdated(const struct flow_offload *flow)
>   {
>   	return test_bit(IPS_SEEN_REPLY_BIT, &flow->ct->status) &&
> +	       test_bit(IPS_HW_OFFLOAD_BIT, &flow->ct->status) &&
> +	       !test_bit(NF_FLOW_HW_PENDING, &flow->flags) &&
>   	       !test_bit(NF_FLOW_HW_ESTABLISHED, &flow->flags);
>   }
>   

Reviewed-by: Paul Blakey <paulb@nvidia.com>