netdev - [PATCH nf-next 4/8] netfilter: nf_flowtable: delay flowtable release a second time

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Date: Tue, 21 Nov 2023 13:27:47 +0100
From: Florian Westphal <fw@...len.de>
To: <netfilter-devel@...r.kernel.org>
Cc: lorenzo@...nel.org,
	<netdev@...r.kernel.org>,
	Florian Westphal <fw@...len.de>
Subject: [PATCH nf-next 4/8] netfilter: nf_flowtable: delay flowtable release a second time

At this time the frontends (tc, nftables) ensure that the nf_flowtable
is removed after the frontend hooks are gone (tc action, netfilter hooks).

In both cases the nf_flowtable can be safely free'd as no packets will
be traversing these hooks anymore.

However, the upcoming nf_flowtable kfunc for XDP will still have a
pointer to the nf_flowtable in its own net_device -> nf_flowtable
mapping.

This mapping is removed via the flow_block UNBIND callback.

This callback however comes after an rcu grace period, not before.

Therefore defer the real freeing via call_rcu so that no kfunc can
possibly be using the nf_flowtable (or flow entries within) anymore.

Signed-off-by: Florian Westphal <fw@...len.de>
---
 include/net/netfilter/nf_flow_table.h |  2 ++
 net/netfilter/nf_flow_table_core.c    | 18 ++++++++++++++----
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/include/net/netfilter/nf_flow_table.h b/include/net/netfilter/nf_flow_table.h
index d365eabd4a3c..6598ac455d17 100644
--- a/include/net/netfilter/nf_flow_table.h
+++ b/include/net/netfilter/nf_flow_table.h
@@ -83,6 +83,8 @@ struct nf_flowtable {
 	struct flow_block		flow_block;
 	struct rw_semaphore		flow_block_lock; /* Guards flow_block */
 	possible_net_t			net;
+
+	struct rcu_work			rwork;
 };
 
 static inline bool nf_flowtable_hw_offload(struct nf_flowtable *flowtable)
diff --git a/net/netfilter/nf_flow_table_core.c b/net/netfilter/nf_flow_table_core.c
index 70cc4e0d5ac9..cae27f8f0f68 100644
--- a/net/netfilter/nf_flow_table_core.c
+++ b/net/netfilter/nf_flow_table_core.c
@@ -599,11 +599,11 @@ void nf_flow_table_cleanup(struct net_device *dev)
 }
 EXPORT_SYMBOL_GPL(nf_flow_table_cleanup);
 
-void nf_flow_table_free(struct nf_flowtable *flow_table)
+static void nf_flow_table_free_rwork(struct work_struct *work)
 {
-	mutex_lock(&flowtable_lock);
-	list_del(&flow_table->list);
-	mutex_unlock(&flowtable_lock);
+	struct nf_flowtable *flow_table;
+
+	flow_table = container_of(to_rcu_work(work), struct nf_flowtable, rwork);
 
 	cancel_delayed_work_sync(&flow_table->gc_work);
 	nf_flow_table_offload_flush(flow_table);
@@ -615,6 +615,16 @@ void nf_flow_table_free(struct nf_flowtable *flow_table)
 	module_put(flow_table->type->owner);
 	kfree(flow_table);
 }
+
+void nf_flow_table_free(struct nf_flowtable *flow_table)
+{
+	mutex_lock(&flowtable_lock);
+	list_del(&flow_table->list);
+	mutex_unlock(&flowtable_lock);
+
+	INIT_RCU_WORK(&flow_table->rwork, nf_flow_table_free_rwork);
+	queue_rcu_work(system_power_efficient_wq, &flow_table->rwork);
+}
 EXPORT_SYMBOL_GPL(nf_flow_table_free);
 
 static int nf_flow_table_init_net(struct net *net)
-- 
2.41.0