From: Cong Wang <redacted>
Date: Tue, 30 Oct 2018 11:09:21 -0700

On Tue, Oct 30, 2018 at 12:57 AM Eric Dumazet [off-list ref] wrote:

quoted

-static __be32 mlx5e_get_fcs(struct sk_buff *skb)
+static u32 mlx5e_get_fcs(const struct sk_buff *skb)
 {
-       int last_frag_sz, bytes_in_prev, nr_frags;
-       u8 *fcs_p1, *fcs_p2;
-       skb_frag_t *last_frag;
-       __be32 fcs_bytes;
+       const void *fcs_bytes;
+       u32 _fcs_bytes;

-       if (!skb_is_nonlinear(skb))
-               return *(__be32 *)(skb->data + skb->len - ETH_FCS_LEN);
+       fcs_bytes = skb_header_pointer(skb, skb->len - ETH_FCS_LEN,
+                                      ETH_FCS_LEN, &_fcs_bytes);

At least skb_header_pointer() is marked as __must_check, I don't see
you check its return value here.

In this case we reasonably know it is guaranteed to succeed though.

We know skb->len is non-zero and we are asking for the skb->len - 1
byte or something like that.