mediatek: prevent duplicate hardware flow offload entries

Signed-off-by: Felix Fietkau <nbd@nbd.name>

target/linux/generic/pending-5.10/700-net-ethernet-mtk_eth_soc-avoid-creating-duplicate-of.patch

@@ -0,0 +1,26 @@
+From: Felix Fietkau <nbd@nbd.name>
+Date: Thu, 8 Jul 2021 07:08:29 +0200
+Subject: [PATCH] net: ethernet: mtk_eth_soc: avoid creating duplicate offload
+ entries
+
+Sometimes multiple CLS_REPLACE calls are issued for the same connection.
+rhashtable_insert_fast does not check for these duplicates, so multiple
+hardware flow entries can be created.
+Fix this by checking for an existing entry early
+
+Fixes: 502e84e2382d ("net: ethernet: mtk_eth_soc: add flow offloading support")
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+---
+
+--- a/drivers/net/ethernet/mediatek/mtk_ppe_offload.c
++++ b/drivers/net/ethernet/mediatek/mtk_ppe_offload.c
+@@ -187,6 +187,9 @@ mtk_flow_offload_replace(struct mtk_eth
+ 	int hash;
+ 	int i;
+
++	if (rhashtable_lookup(&eth->flow_table, &f->cookie, mtk_flow_ht_params))
++		return -EEXIST;
++
+ 	if (flow_rule_match_key(rule, FLOW_DISSECTOR_KEY_META)) {
+ 		struct flow_match_meta match;
+