sfc: keep alive neighbour entries while a TC encap action is using them

When processing counter updates, if any action set using the newly
 incremented counter includes an encap action, prod the corresponding
 neighbouring entry to indicate to the neighbour cache that the entry
 is still in use and passing traffic.

Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
Link: https://lore.kernel.org/r/20230621121504.17004-1-edward.cree@amd.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/sfc/tc.c

@@ -110,8 +110,13 @@ static void efx_tc_free_action_set(struct efx_nic *efx,
 		 */
 		list_del(&act->list);
 	}
-	if (act->count)
+	if (act->count) {
+		spin_lock_bh(&act->count->cnt->lock);
+		if (!list_empty(&act->count_user))
+			list_del(&act->count_user);
+		spin_unlock_bh(&act->count->cnt->lock);
 		efx_tc_flower_put_counter_index(efx, act->count);
+	}
 	if (act->encap_md) {
 		list_del(&act->encap_user);
 		efx_tc_flower_release_encap_md(efx, act->encap_md);
@@ -796,6 +801,7 @@ static int efx_tc_flower_replace_foreign(struct efx_nic *efx,
 					goto release;
 				}
 				act->count = ctr;
+				INIT_LIST_HEAD(&act->count_user);
 			}
 
 			if (!efx_tc_flower_action_order_ok(act, EFX_TC_AO_DELIVER)) {
@@ -1083,6 +1089,7 @@ static int efx_tc_flower_replace(struct efx_nic *efx,
 				goto release;
 			}
 			act->count = ctr;
+			INIT_LIST_HEAD(&act->count_user);
 		}
 
 		switch (fa->id) {
@@ -1120,6 +1127,17 @@ static int efx_tc_flower_replace(struct efx_nic *efx,
 				list_add_tail(&act->encap_user, &encap->users);
 				act->dest_mport = encap->dest_mport;
 				act->deliver = 1;
+				if (act->count && !WARN_ON(!act->count->cnt)) {
+					/* This counter is used by an encap
+					 * action, which needs a reference back
+					 * so it can prod neighbouring whenever
+					 * traffic is seen.
+					 */
+					spin_lock_bh(&act->count->cnt->lock);
+					list_add_tail(&act->count_user,
+						      &act->count->cnt->users);
+					spin_unlock_bh(&act->count->cnt->lock);
+				}
 				rc = efx_mae_alloc_action_set(efx, act);
 				if (rc) {
 					NL_SET_ERR_MSG_MOD(extack, "Failed to write action set to hw (encap)");

drivers/net/ethernet/sfc/tc.h

@@ -38,6 +38,7 @@ struct efx_tc_action_set {
 	struct efx_tc_encap_action *encap_md; /* entry in tc_encap_ht table */
 	struct list_head encap_user; /* entry on encap_md->users list */
 	struct efx_tc_action_set_list *user; /* Only populated if encap_md */
+	struct list_head count_user; /* entry on counter->users list, if encap */
 	u32 dest_mport;
 	u32 fw_id; /* index of this entry in firmware actions table */
 	struct list_head list;

drivers/net/ethernet/sfc/tc_counters.c

@@ -9,6 +9,7 @@
  */
 
 #include "tc_counters.h"
+#include "tc_encap_actions.h"
 #include "mae_counter_format.h"
 #include "mae.h"
 #include "rx_common.h"
@@ -31,6 +32,15 @@ static void efx_tc_counter_free(void *ptr, void *__unused)
 {
 	struct efx_tc_counter *cnt = ptr;
 
+	WARN_ON(!list_empty(&cnt->users));
+	/* We'd like to synchronize_rcu() here, but unfortunately we aren't
+	 * removing the element from the hashtable (it's not clear that's a
+	 * safe thing to do in an rhashtable_free_and_destroy free_fn), so
+	 * threads could still be obtaining new pointers to *cnt if they can
+	 * race against this function at all.
+	 */
+	flush_work(&cnt->work);
+	EFX_WARN_ON_PARANOID(spin_is_locked(&cnt->lock));
 	kfree(cnt);
 }
 
@@ -74,6 +84,49 @@ void efx_tc_fini_counters(struct efx_nic *efx)
 	rhashtable_free_and_destroy(&efx->tc->counter_ht, efx_tc_counter_free, NULL);
 }
 
+static void efx_tc_counter_work(struct work_struct *work)
+{
+	struct efx_tc_counter *cnt = container_of(work, struct efx_tc_counter, work);
+	struct efx_tc_encap_action *encap;
+	struct efx_tc_action_set *act;
+	unsigned long touched;
+	struct neighbour *n;
+
+	spin_lock_bh(&cnt->lock);
+	touched = READ_ONCE(cnt->touched);
+
+	list_for_each_entry(act, &cnt->users, count_user) {
+		encap = act->encap_md;
+		if (!encap)
+			continue;
+		if (!encap->neigh) /* can't happen */
+			continue;
+		if (time_after_eq(encap->neigh->used, touched))
+			continue;
+		encap->neigh->used = touched;
+		/* We have passed traffic using this ARP entry, so
+		 * indicate to the ARP cache that it's still active
+		 */
+		if (encap->neigh->dst_ip)
+			n = neigh_lookup(&arp_tbl, &encap->neigh->dst_ip,
+					 encap->neigh->egdev);
+		else
+#if IS_ENABLED(CONFIG_IPV6)
+			n = neigh_lookup(ipv6_stub->nd_tbl,
+					 &encap->neigh->dst_ip6,
+					 encap->neigh->egdev);
+#else
+			n = NULL;
+#endif
+		if (!n)
+			continue;
+
+		neigh_event_send(n, NULL);
+		neigh_release(n);
+	}
+	spin_unlock_bh(&cnt->lock);
+}
+
 /* Counter allocation */
 
 static struct efx_tc_counter *efx_tc_flower_allocate_counter(struct efx_nic *efx,
@@ -87,12 +140,14 @@ static struct efx_tc_counter *efx_tc_flower_allocate_counter(struct efx_nic *efx
 		return ERR_PTR(-ENOMEM);
 
 	spin_lock_init(&cnt->lock);
+	INIT_WORK(&cnt->work, efx_tc_counter_work);
 	cnt->touched = jiffies;
 	cnt->type = type;
 
 	rc = efx_mae_allocate_counter(efx, cnt);
 	if (rc)
 		goto fail1;
+	INIT_LIST_HEAD(&cnt->users);
 	rc = rhashtable_insert_fast(&efx->tc->counter_ht, &cnt->linkage,
 				    efx_tc_counter_ht_params);
 	if (rc)
@@ -126,6 +181,7 @@ static void efx_tc_flower_release_counter(struct efx_nic *efx,
 		netif_warn(efx, hw, efx->net_dev,
 			   "Failed to free MAE counter %u, rc %d\n",
 			   cnt->fw_id, rc);
+	WARN_ON(!list_empty(&cnt->users));
 	/* This doesn't protect counter updates coming in arbitrarily long
 	 * after we deleted the counter.  The RCU just ensures that we won't
 	 * free the counter while another thread has a pointer to it.
@@ -133,6 +189,7 @@ static void efx_tc_flower_release_counter(struct efx_nic *efx,
 	 * is handled by the generation count.
 	 */
 	synchronize_rcu();
+	flush_work(&cnt->work);
 	EFX_WARN_ON_PARANOID(spin_is_locked(&cnt->lock));
 	kfree(cnt);
 }
@@ -302,6 +359,7 @@ static void efx_tc_counter_update(struct efx_nic *efx,
 		cnt->touched = jiffies;
 	}
 	spin_unlock_bh(&cnt->lock);
+	schedule_work(&cnt->work);
 out:
 	rcu_read_unlock();
 }

drivers/net/ethernet/sfc/tc_counters.h

@@ -32,6 +32,9 @@ struct efx_tc_counter {
 	u64 old_packets, old_bytes; /* Values last time passed to userspace */
 	/* jiffies of the last time we saw packets increase */
 	unsigned long touched;
+	struct work_struct work; /* For notifying encap actions */
+	/* owners of corresponding count actions */
+	struct list_head users;
 };
 
 struct efx_tc_counter_index {