gso: Validate assumption of frag_list segementation

Commit 07b26c9454a2 ("gso: Support partial splitting at the frag_list
pointer") assumes that all SKBs in a frag_list (except maybe the last
one) contain the same amount of GSO payload.

This assumption is not always correct, resulting in the following
warning message in the log:
    skb_segment: too many frags

For example, mlx5 driver in Striding RQ mode creates some RX SKBs with
one frag, and some with 2 frags.
After GRO, the frag_list SKBs end up having different amounts of payload.
If this frag_list SKB is then forwarded, the aforementioned assumption
is violated.

Validate the assumption, and fall back to software GSO if it not true.

Change-Id: Ia03983f4a47b6534dd987d7a2aad96d54d46d212
Fixes: 07b26c9454a2 ("gso: Support partial splitting at the frag_list pointer")
Signed-off-by: Ilan Tayari <ilant@mellanox.com>
Signed-off-by: Ilya Lesokhin <ilyal@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 35c1e24..f86bf69 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3082,22 +3082,32 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
        if (sg && csum && (mss != GSO_BY_FRAGS))  {
                if (!(features & NETIF_F_GSO_PARTIAL)) {
                        struct sk_buff *iter;
+                       unsigned int frag_len;
 
                        if (!list_skb ||
                            !net_gso_ok(features, skb_shinfo(head_skb)->gso_type))
                                goto normal;
 
-                       /* Split the buffer at the frag_list pointer.
-                        * This is based on the assumption that all
-                        * buffers in the chain excluding the last
-                        * containing the same amount of data.
+                       /* If we get here then all the required
+                        * GSO features except frag_list are supported.
+                        * Try to split the SKB to multiple GSO SKBs
+                        * with no frag_list.
+                        * Currently we can do that only when the buffers don't
+                        * have a linear part and all the buffers except
+                        * the last are of the same length.
                         */
+                       frag_len = list_skb->len;
                        skb_walk_frags(head_skb, iter) {
+                               if (frag_len != iter->len && iter->next)
+                                       goto normal;
                                if (skb_headlen(iter))
                                        goto normal;
 
                                len -= iter->len;
                        }
+
+                       if (len != frag_len)
+                               goto normal;
                }
 
                /* GSO partial only requires that we trim off any excess that