xen-netback: Fix handling frag_list on grant op error path

The error handling for skb's with frag_list was completely wrong, it caused
double unmap attempts to happen if the error was on the first skb. Move it to
the right place in the loop.

Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com>
Reported-by: Armin Zentai <armin.zentai@ezit.hu>
Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: xen-devel@lists.xenproject.org
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 20 insertions, 17 deletions

diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 1844a47636b6..a773f2016bad 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -1030,10 +1030,16 @@ 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;
         int i, err;
-        struct sk_buff *first_skb = NULL;
 
         /* Check status of header. */
         err = (*gopp_copy)->status;
@@ -1086,31 +1092,28 @@ check_frags:
                         xenvif_idx_unmap(queue, pending_idx);
                 }
 
+                /* 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);
+                        }
+                }
+
                 /* 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;
 }