RDMA/rxe: Fix extra deref in rxe_rcv_mcast_pkt()

rxe_rcv_mcast_pkt() dropped a reference to ib_device when no error
occurred causing an underflow on the reference counter.  This code is
cleaned up to be clearer and easier to read.

Fixes: 899aba891cab ("RDMA/rxe: Fix FIXME in rxe_udp_encap_recv()")
Link: https://lore.kernel.org/r/20210304192048.2958-1-rpearson@hpe.com
Signed-off-by: Bob Pearson <rpearsonhpe@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

diff --git a/drivers/infiniband/sw/rxe/rxe_recv.c b/drivers/infiniband/sw/rxe/rxe_recv.c
index 45d2f71..7a49e27 100644 (file)
--- a/drivers/infiniband/sw/rxe/rxe_recv.c
+++ b/drivers/infiniband/sw/rxe/rxe_recv.c
@@ -237,8 +237,6 @@ static void rxe_rcv_mcast_pkt(struct rxe_dev *rxe, struct sk_buff *skb)
        struct rxe_mc_elem *mce;
        struct rxe_qp *qp;
        union ib_gid dgid;
-       struct sk_buff *per_qp_skb;
-       struct rxe_pkt_info *per_qp_pkt;
        int err;
 
        if (skb->protocol == htons(ETH_P_IP))
@@ -250,10 +248,15 @@ static void rxe_rcv_mcast_pkt(struct rxe_dev *rxe, struct sk_buff *skb)
        /* lookup mcast group corresponding to mgid, takes a ref */
        mcg = rxe_pool_get_key(&rxe->mc_grp_pool, &dgid);
        if (!mcg)
-               goto err1;      /* mcast group not registered */
+               goto drop;      /* mcast group not registered */
 
        spin_lock_bh(&mcg->mcg_lock);
 
+       /* this is unreliable datagram service so we let
+        * failures to deliver a multicast packet to a
+        * single QP happen and just move on and try
+        * the rest of them on the list
+        */
        list_for_each_entry(mce, &mcg->qp_list, qp_list) {
                qp = mce->qp;
 
@@ -266,39 +269,47 @@ static void rxe_rcv_mcast_pkt(struct rxe_dev *rxe, struct sk_buff *skb)
                if (err)
                        continue;
 
-               /* for all but the last qp create a new clone of the
-                * skb and pass to the qp. If an error occurs in the
-                * checks for the last qp in the list we need to
-                * free the skb since it hasn't been passed on to
-                * rxe_rcv_pkt() which would free it later.
+               /* for all but the last QP create a new clone of the
+                * skb and pass to the QP. Pass the original skb to
+                * the last QP in the list.
                 */
                if (mce->qp_list.next != &mcg->qp_list) {
-                       per_qp_skb = skb_clone(skb, GFP_ATOMIC);
-                       if (WARN_ON(!ib_device_try_get(&rxe->ib_dev))) {
-                               kfree_skb(per_qp_skb);
+                       struct sk_buff *cskb;
+                       struct rxe_pkt_info *cpkt;
+
+                       cskb = skb_clone(skb, GFP_ATOMIC);
+                       if (unlikely(!cskb))
                                continue;
+
+                       if (WARN_ON(!ib_device_try_get(&rxe->ib_dev))) {
+                               kfree_skb(cskb);
+                               break;
                        }
+
+                       cpkt = SKB_TO_PKT(cskb);
+                       cpkt->qp = qp;
+                       rxe_add_ref(qp);
+                       rxe_rcv_pkt(cpkt, cskb);
                } else {
-                       per_qp_skb = skb;
-                       /* show we have consumed the skb */
-                       skb = NULL;
+                       pkt->qp = qp;
+                       rxe_add_ref(qp);
+                       rxe_rcv_pkt(pkt, skb);
+                       skb = NULL;     /* mark consumed */
                }
-
-               if (unlikely(!per_qp_skb))
-                       continue;
-
-               per_qp_pkt = SKB_TO_PKT(per_qp_skb);
-               per_qp_pkt->qp = qp;
-               rxe_add_ref(qp);
-               rxe_rcv_pkt(per_qp_pkt, per_qp_skb);
        }
 
        spin_unlock_bh(&mcg->mcg_lock);
 
        rxe_drop_ref(mcg);      /* drop ref from rxe_pool_get_key. */
 
-err1:
-       /* free skb if not consumed */
+       if (likely(!skb))
+               return;
+
+       /* This only occurs if one of the checks fails on the last
+        * QP in the list above
+        */
+
+drop:
        kfree_skb(skb);
        ib_device_put(&rxe->ib_dev);
 }