Re: [Xen-devel] compound skb frag pages appearing in start_xmit

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2012-10-10 at 11:13 +0100, Ian Campbell wrote:
> I haven't tackled netfront yet. 

I seem to be totally unable to reproduce the equivalent issue on the
netfront xmit side, even though it seems like the loop in
xennet_make_frags ought to be obviously susceptible to it.

Konrad, Sander, are either of you able to repro, e.g. with:

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index b06ef81..8a3f770 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -462,6 +462,8 @@ static void xennet_make_frags(struct sk_buff *skb, struct 
net_device *dev,
                ref = gnttab_claim_grant_reference(&np->gref_tx_head);
                BUG_ON((signed short)ref < 0);
 
+               BUG_ON(PageCompound(skb_frag_page(frag)));
+
                mfn = pfn_to_mfn(page_to_pfn(skb_frag_page(frag)));
                gnttab_grant_foreign_access_ref(ref, np->xbdev->otherend_id,
                                                mfn, GNTMAP_readonly);

My repro for netback was just to netcat a wodge of data from dom0->domU
but going the other way doesn't seem to trigger.


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