1 files changed, 63 insertions, 23 deletions

diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 1844a47..c65b636 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -1030,14 +1030,21 @@ static int xenvif_tx_check_gop(struct xenvif_queue *queue,
 {
 	struct gnttab_map_grant_ref *gop_map = *gopp_map;
 	u16 pending_idx = XENVIF_TX_CB(skb)->pending_idx;
+	/* This always points to the shinfo of the skb being checked, which
+	 * could be either the first or the one on the frag_list
+	 */
 	struct skb_shared_info *shinfo = skb_shinfo(skb);
+	/* If this is non-NULL, we are currently checking the frag_list skb, and
+	 * this points to the shinfo of the first one
+	 */
+	struct skb_shared_info *first_shinfo = NULL;
 	int nr_frags = shinfo->nr_frags;
+	const bool sharedslot = nr_frags &&
+				frag_get_pending_idx(&shinfo->frags[0]) == pending_idx;
 	int i, err;
-	struct sk_buff *first_skb = NULL;
 
 	/* Check status of header. */
 	err = (*gopp_copy)->status;
-	(*gopp_copy)++;
 	if (unlikely(err)) {
 		if (net_ratelimit())
 			netdev_dbg(queue->vif->dev,
@@ -1045,8 +1052,12 @@ static int xenvif_tx_check_gop(struct xenvif_queue *queue,
 				   (*gopp_copy)->status,
 				   pending_idx,
 				   (*gopp_copy)->source.u.ref);
-		xenvif_idx_release(queue, pending_idx, XEN_NETIF_RSP_ERROR);
+		/* The first frag might still have this slot mapped */
+		if (!sharedslot)
+			xenvif_idx_release(queue, pending_idx,
+					   XEN_NETIF_RSP_ERROR);
 	}
+	(*gopp_copy)++;
 
 check_frags:
 	for (i = 0; i < nr_frags; i++, gop_map++) {
@@ -1062,8 +1073,19 @@ check_frags:
 						pending_idx,
 						gop_map->handle);
 			/* Had a previous error? Invalidate this fragment. */
-			if (unlikely(err))
+			if (unlikely(err)) {
 				xenvif_idx_unmap(queue, pending_idx);
+				/* If the mapping of the first frag was OK, but
+				 * the header's copy failed, and they are
+				 * sharing a slot, send an error
+				 */
+				if (i == 0 && sharedslot)
+					xenvif_idx_release(queue, pending_idx,
+							   XEN_NETIF_RSP_ERROR);
+				else
+					xenvif_idx_release(queue, pending_idx,
+							   XEN_NETIF_RSP_OKAY);
+			}
 			continue;
 		}
 
@@ -1075,42 +1097,53 @@ check_frags:
 				   gop_map->status,
 				   pending_idx,
 				   gop_map->ref);
+
 		xenvif_idx_release(queue, pending_idx, XEN_NETIF_RSP_ERROR);
 
 		/* Not the first error? Preceding frags already invalidated. */
 		if (err)
 			continue;
-		/* First error: invalidate preceding fragments. */
+
+		/* First error: if the header haven't shared a slot with the
+		 * first frag, release it as well.
+		 */
+		if (!sharedslot)
+			xenvif_idx_release(queue,
+					   XENVIF_TX_CB(skb)->pending_idx,
+					   XEN_NETIF_RSP_OKAY);
+
+		/* Invalidate preceding fragments of this skb. */
 		for (j = 0; j < i; j++) {
 			pending_idx = frag_get_pending_idx(&shinfo->frags[j]);
 			xenvif_idx_unmap(queue, pending_idx);
+			xenvif_idx_release(queue, pending_idx,
+					   XEN_NETIF_RSP_OKAY);
+		}
+
+		/* And if we found the error while checking the frag_list, unmap
+		 * the first skb's frags
+		 */
+		if (first_shinfo) {
+			for (j = 0; j < first_shinfo->nr_frags; j++) {
+				pending_idx = frag_get_pending_idx(&first_shinfo->frags[j]);
+				xenvif_idx_unmap(queue, pending_idx);
+				xenvif_idx_release(queue, pending_idx,
+						   XEN_NETIF_RSP_OKAY);
+			}
 		}
 
 		/* Remember the error: invalidate all subsequent fragments. */
 		err = newerr;
 	}
 
-	if (skb_has_frag_list(skb)) {
-		first_skb = skb;
-		skb = shinfo->frag_list;
-		shinfo = skb_shinfo(skb);
+	if (skb_has_frag_list(skb) && !first_shinfo) {
+		first_shinfo = skb_shinfo(skb);
+		shinfo = skb_shinfo(skb_shinfo(skb)->frag_list);
 		nr_frags = shinfo->nr_frags;
 
 		goto check_frags;
 	}
 
-	/* There was a mapping error in the frag_list skb. We have to unmap
-	 * the first skb's frags
-	 */
-	if (first_skb && err) {
-		int j;
-		shinfo = skb_shinfo(first_skb);
-		for (j = 0; j < shinfo->nr_frags; j++) {
-			pending_idx = frag_get_pending_idx(&shinfo->frags[j]);
-			xenvif_idx_unmap(queue, pending_idx);
-		}
-	}
-
 	*gopp_map = gop_map;
 	return err;
 }
@@ -1518,7 +1551,16 @@ static int xenvif_tx_submit(struct xenvif_queue *queue)
 
 		/* Check the remap error code. */
 		if (unlikely(xenvif_tx_check_gop(queue, skb, &gop_map, &gop_copy))) {
+			/* If there was an error, xenvif_tx_check_gop is
+			 * expected to release all the frags which were mapped,
+			 * so kfree_skb shouldn't do it again
+			 */
 			skb_shinfo(skb)->nr_frags = 0;
+			if (skb_has_frag_list(skb)) {
+				struct sk_buff *nskb =
+						skb_shinfo(skb)->frag_list;
+				skb_shinfo(nskb)->nr_frags = 0;
+			}
 			kfree_skb(skb);
 			continue;
 		}
@@ -1822,8 +1864,6 @@ void xenvif_idx_unmap(struct xenvif_queue *queue, u16 pending_idx)
 			   tx_unmap_op.status);
 		BUG();
 	}
-
-	xenvif_idx_release(queue, pending_idx, XEN_NETIF_RSP_OKAY);
 }
 
 static inline int rx_work_todo(struct xenvif_queue *queue)