mctp: Return new key from mctp_alloc_local_tag

In a future change, we will want the key available for future use after
allocating a new tag. This change returns the key from
mctp_alloc_local_tag, rather than just key->tag.
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/mctp/route.c

@@ -532,14 +532,14 @@ static void mctp_reserve_tag(struct net *net, struct mctp_sk_key *key,
 /* Allocate a locally-owned tag value for (saddr, daddr), and reserve
  * it for the socket msk
  */
-static int mctp_alloc_local_tag(struct mctp_sock *msk,
-				mctp_eid_t saddr, mctp_eid_t daddr, u8 *tagp)
+static struct mctp_sk_key *mctp_alloc_local_tag(struct mctp_sock *msk,
+						mctp_eid_t saddr,
+						mctp_eid_t daddr, u8 *tagp)
 {
 	struct net *net = sock_net(&msk->sk);
 	struct netns_mctp *mns = &net->mctp;
 	struct mctp_sk_key *key, *tmp;
 	unsigned long flags;
-	int rc = -EAGAIN;
 	u8 tagbits;
 
 	/* for NULL destination EIDs, we may get a response from any peer */
@@ -549,7 +549,7 @@ static int mctp_alloc_local_tag(struct mctp_sock *msk,
 	/* be optimistic, alloc now */
 	key = mctp_key_alloc(msk, saddr, daddr, 0, GFP_KERNEL);
 	if (!key)
-		return -ENOMEM;
+		return ERR_PTR(-ENOMEM);
 
 	/* 8 possible tag values */
 	tagbits = 0xff;
@@ -591,18 +591,16 @@ static int mctp_alloc_local_tag(struct mctp_sock *msk,
 		trace_mctp_key_acquire(key);
 
 		*tagp = key->tag;
-		/* done with the key in this scope */
-		mctp_key_unref(key);
-		key = NULL;
-		rc = 0;
 	}
 
 	spin_unlock_irqrestore(&mns->keys_lock, flags);
 
-	if (!tagbits)
+	if (!tagbits) {
 		kfree(key);
+		return ERR_PTR(-EBUSY);
+	}
 
-	return rc;
+	return key;
 }
 
 /* routing lookups */
@@ -740,6 +738,7 @@ int mctp_local_output(struct sock *sk, struct mctp_route *rt,
 	struct mctp_sock *msk = container_of(sk, struct mctp_sock, sk);
 	struct mctp_skb_cb *cb = mctp_cb(skb);
 	struct mctp_route tmp_rt;
+	struct mctp_sk_key *key;
 	struct net_device *dev;
 	struct mctp_hdr *hdr;
 	unsigned long flags;
@@ -799,11 +798,16 @@ int mctp_local_output(struct sock *sk, struct mctp_route *rt,
 		goto out_release;
 
 	if (req_tag & MCTP_HDR_FLAG_TO) {
-		rc = mctp_alloc_local_tag(msk, saddr, daddr, &tag);
-		if (rc)
+		key = mctp_alloc_local_tag(msk, saddr, daddr, &tag);
+		if (IS_ERR(key)) {
+			rc = PTR_ERR(key);
 			goto out_release;
+		}
+		/* done with the key in this scope */
+		mctp_key_unref(key);
 		tag |= MCTP_HDR_FLAG_TO;
 	} else {
+		key = NULL;
 		tag = req_tag;
 	}