xen/netback: Calculate the number of SKB slots required correctly

When calculating the number of slots required for a packet header, the code
was reserving too many slots if the header crossed a page boundary. Since
netbk_gop_skb copies the header to the start of the page, the count of
slots required for the header should be based solely on the header size.

This problem is easy to reproduce if a VIF is bridged to a USB 3G modem
device as the skb->data value always starts near the end of the first page.

Signed-off-by: Simon Graham <simon.graham@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 2596401308a86e24210efd65d531d91d6be60746..f4a6fcaeffb1db381ef9fd007a72578d984a3b4c 100644 (file)
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -325,8 +325,7 @@ unsigned int xen_netbk_count_skb_slots(struct xenvif *vif, struct sk_buff *skb)
        unsigned int count;
        int i, copy_off;
 
-       count = DIV_ROUND_UP(
-                       offset_in_page(skb->data)+skb_headlen(skb), PAGE_SIZE);
+       count = DIV_ROUND_UP(skb_headlen(skb), PAGE_SIZE);
 
        copy_off = skb_headlen(skb) % PAGE_SIZE;