Re: [Xen-devel] netback Oops then xenwatch stuck in D state

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Feb 13, 2013 at 07:20:32PM +0000, David Vrabel wrote:
> On 13/02/13 18:37, Wei Liu wrote:
> > A slightly upgraded version of the *UNTESTED* patch.
> > 
> > 
> > Wei.
> > 
> > ----8<----
> > commit df4c929d034cec7043fbd96ba89833eb639c336e
> > Author: Wei Liu <wei.liu2@xxxxxxxxxx>
> > Date:   Wed Feb 13 18:17:01 2013 +0000
> > 
> >     netback: fix netbk_count_requests
> >     
> >     There are two paths in the original code, a) test against work_to_do, 
> > b) test
> >     against first->size, could return 0 even when error happens.
> >     
> >     Simply return -1 in error paths should work. Modify all error paths to 
> > return
> >     -1 to be consistent.
> 
> You also need to remove the netbk_tx_err() after checking the result of
> netbk_count_requests().  Otherwise you will have a double xenvif_put(),
> which will screw up ref counting.

I just realized that we were talking about different code path when I
walked home.

The path you mentioned is correct. As excution flow should never reach
there if there is error in netbk_count_requests.

The path I'm not sure is that in the netbk_fatal_tx_err, it calls
xenvif_carrier_off which calls xenvif_put, and then it calls xenvif_put,
which is likely to mess up the refcount.


Wei.

> 
> I would also suggest returning -EINVAL from netbk_count_requests().
> 
> It not clear to me how this will fix the original oops though.
> 
> David
> 
> >     
> >     Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> > 
> > diff --git a/drivers/net/xen-netback/netback.c 
> > b/drivers/net/xen-netback/netback.c
> > index 103294d..0e0162e 100644
> > --- a/drivers/net/xen-netback/netback.c
> > +++ b/drivers/net/xen-netback/netback.c
> > @@ -913,13 +913,13 @@ static int netbk_count_requests(struct xenvif *vif,
> >             if (frags >= work_to_do) {
> >                     netdev_err(vif->dev, "Need more frags\n");
> >                     netbk_fatal_tx_err(vif);
> > -                   return -frags;
> > +                   return -1;
> >             }
> >  
> >             if (unlikely(frags >= MAX_SKB_FRAGS)) {
> >                     netdev_err(vif->dev, "Too many frags\n");
> >                     netbk_fatal_tx_err(vif);
> > -                   return -frags;
> > +                   return -1;
> >             }
> >  
> >             memcpy(txp, RING_GET_REQUEST(&vif->tx, cons + frags),
> > @@ -927,7 +927,7 @@ static int netbk_count_requests(struct xenvif *vif,
> >             if (txp->size > first->size) {
> >                     netdev_err(vif->dev, "Frag is bigger than frame.\n");
> >                     netbk_fatal_tx_err(vif);
> > -                   return -frags;
> > +                   return -1;
> >             }
> >  
> >             first->size -= txp->size;
> > @@ -937,7 +937,7 @@ static int netbk_count_requests(struct xenvif *vif,
> >                     netdev_err(vif->dev, "txp->offset: %x, size: %u\n",
> >                              txp->offset, txp->size);
> >                     netbk_fatal_tx_err(vif);
> > -                   return -frags;
> > +                   return -1;
> >             }
> >     } while ((txp++)->flags & XEN_NETTXF_more_data);
> >     return frags;
> > 
> > 
> > 
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxx
> > http://lists.xen.org/xen-devel
> 

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