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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2012-10-10 at 15:49 +0100, Sander Eikelenboom wrote:
> Wednesday, October 10, 2012, 3:09:58 PM, you wrote:
> 
> > 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:
> 
> 
> Hmrrrmm i don't see any traces, only strange behaviour ..
> 
> - i can connect to guests by ssh, but it's sluggish, and sometimes stops 
> working

I saw something like this (ssh sluggish) even with dom0 itself. I'm
trying to see if I can characterise it enough to reliably bisect it.

I already switched out xen-unstable for 4.2-testing but that didn't make
any difference.

> - The guest seem to keep trying to connect to netback:
> 
> [  658.276719] xen_bridge: port 2(vif40.0) entered forwarding state
> [  658.282258] xen_bridge: port 2(vif40.0) entered forwarding state
> [  663.945964] xen_bridge: port 7(vif39.0) entered forwarding state
> [  669.674277] xen_bridge: port 2(vif40.0) entered disabled state
> [  669.680290] device vif40.0 left promiscuous mode
> [  669.685464] xen_bridge: port 2(vif40.0) entered disabled state
> [  672.857222] device vif41.0 entered promiscuous mode
> [  673.166254] xen-blkback:ring-ref 8, event-channel 9, protocol 1 
> (x86_64-abi)
> [  673.176368] xen_bridge: port 2(vif41.0) entered forwarding state
> [  673.182042] xen_bridge: port 2(vif41.0) entered forwarding state
> [  674.439725] xen_bridge: port 7(vif39.0) entered disabled state
> [  674.445708] device vif39.0 left promiscuous mode
> [  674.450955] xen_bridge: port 7(vif39.0) entered disabled state
> [  677.726040] device vif42.0 entered promiscuous mode
> [  678.053381] xen-blkback:ring-ref 8, event-channel 9, protocol 1 
> (x86_64-abi)
> [  678.062804] xen_bridge: port 7(vif42.0) entered forwarding state
> [  678.068433] xen_bridge: port 7(vif42.0) entered forwarding state
> [  688.224736] xen_bridge: port 2(vif41.0) entered forwarding state
> [  693.080557] xen_bridge: port 7(vif42.0) entered forwarding state
> [  700.786276] xen_bridge: port 7(vif42.0) entered disabled state
> [  700.792484] device vif42.0 left promiscuous mode
> [  700.802409] xen_bridge: port 7(vif42.0) entered disabled state
> [  704.133606] device vif43.0 entered promiscuous mode
> [  704.460160] xen-blkback:ring-ref 8, event-channel 9, protocol 1 
> (x86_64-abi)
> [  704.469800] xen_bridge: port 7(vif43.0) entered forwarding state
> [  704.475303] xen_bridge: port 7(vif43.0) entered forwarding state
> [  719.493788] xen_bridge: port 7(vif43.0) entered forwarding state
> [  726.302456] xen_bridge: port 7(vif43.0) entered disabled state
> [  726.308898] device vif43.0 left promiscuous mode
> [  726.314029] xen_bridge: port 7(vif43.0) entered disabled state
> 
> All the guests are already up, but this keeps on going and going and going 
> ....

The domain number seems to be climbing, are you sure something isn't
(crashing and) restarting?

> > 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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