RE: [Xen-devel] network hang trigger

["James Harper" <JamesH@xxxxxxxxxxxxxxxx>]

I see this problem after 1 ping of size > MTU (which probably explains
why NFS hangs too!). If I understand correctly, the situation you
describe should only come about if an error occurs for other reasons.

So do we still have another outstanding bug?

Thanks

James

> -----Original Message-----
> From: xen-devel-admin@xxxxxxxxxxxxxxxxxxxxx [mailto:xen-devel-
> admin@xxxxxxxxxxxxxxxxxxxxx] On Behalf Of Bin Ren
> Sent: Thursday, 16 September 2004 08:11
> To: xen-devel@xxxxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-devel] network hang trigger
> 
> Here is what I find out:
> 
> In netfront.c, the transmit function is:
> 
> network_start_xmit(struct sk_buff *skb, struct net_device *dev)
> 
> Currently, whenever there is an error, it returns 1 or -ENOBUFS
> ***WITHOUT*** freeing the ***skb***. This is based on the assumption
that
> the caller, seeing a non-zero return value, will free the ***skb***.
Let's
> take a look at the caller:
> 
> int dev_queue_xmit(struct sk_buff *skb)
> 
> in file net/core.c
> ======================================
> if (!dev->hard_start_xmit(skb, dev)) {
>         HARD_TX_UNLOCK_BH(dev);
>         goto out;
> }
> ...
> 
> out_kfree_skb:
>         kfree_skb(skb);
> out:
>         return rc;
> ======================================
> 
> Bingo, it doesn't. And take a look at other network driver source
codes,
> e.g. 8139too.c, 3c501.c etc, they all ***free skb*** upon error and
> ***always return 0***. This is *hidden contract* between the caller
and
> the
> callee.
> 
> So, skbuffs don't get freed until gc'ed.
> 
> I'm going to modify the files and see the result.
> Keep tuned.
> 
> -- Bin Ren
> 
> 
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