flow_dissector: Ignore flow dissector return value from ___skb_get_hash

In ___skb_get_hash ignore return value from skb_flow_dissect_flow_keys.
A failure in that function likely means that there was a parse error,
so we may as well use whatever fields were found before the error was
hit.  This is also good because it means we won't keep trying to derive
the hash on subsequent calls to skb_get_hash for the same packet.
Signed-off-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/flow_dissector.c

@@ -616,9 +616,8 @@ EXPORT_SYMBOL(flow_hash_from_keys);
 static inline u32 ___skb_get_hash(const struct sk_buff *skb,
 				  struct flow_keys *keys, u32 keyval)
 {
-	if (!skb_flow_dissect_flow_keys(skb, keys,
-					FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL))
-		return 0;
+	skb_flow_dissect_flow_keys(skb, keys,
+				   FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL);
 
 	return __flow_hash_from_keys(keys, keyval);
 }
@@ -662,15 +661,10 @@ EXPORT_SYMBOL(make_flow_keys_digest);
 void __skb_get_hash(struct sk_buff *skb)
 {
 	struct flow_keys keys;
-	u32 hash;
 
 	__flow_hash_secret_init();
 
-	hash = ___skb_get_hash(skb, &keys, hashrnd);
-	if (!hash)
-		return;
-
-	__skb_set_sw_hash(skb, hash,
+	__skb_set_sw_hash(skb, ___skb_get_hash(skb, &keys, hashrnd),
 			  flow_keys_have_l4(&keys));
 }
 EXPORT_SYMBOL(__skb_get_hash);