Re: [Xen-devel] PV DomU running linux 3.17.3 causing xen-netback fatal error in Dom0

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 28/11/14 15:19, Anthony Wright wrote:
> We have a 64 bit PV DomU that we recently upgraded from linux 3.3.2 to
> 3.17.3 running on a 64 bit 3.17.3 Dom0 with Xen 4.4.0.
> 
> Shortly after the upgrade we started to lose network connectivity to the
> DomU a few times a day that required a reboot to fix. We see nothing in
> the xen logs or xl dmesg, but when we looked at the dmesg output we saw
> the following output for the two incidents we investigated in detail:
> 
> [69332.026586] vif vif-4-0 vif4.0: txreq.offset: 85e, size: 4002, end: 6144
> [69332.026607] vif vif-4-0 vif4.0: fatal error; disabling device
> [69332.031069] br-default: port 2(vif4.0) entered disabled state
> 
> 
> [824365.530740] vif vif-9-0 vif9.0: txreq.offset: a5e, size: 4002, end: 6656
> [824365.530748] vif vif-9-0 vif9.0: fatal error; disabling device
> [824365.531191] br-default: port 2(vif9.0) entered disabled state
> 
> We have a very similar setup running on another machine with a 3.17.3
> DomU, 3.17.3 Dom0 and Xen 4.4.0 but we can't reproduce the issue on this
> machine. This is a test system rather than a production system so has a
> different workload and fewer CPUs.
> 
> The piece of code that outputs the error is in
> drivers/net/xen-netback/netback.c.

Does this patch to netfront fix it?

8<---------------------------------------------
xen-netfront: use correct linear area after linearizing an skb

Commit 97a6d1bb2b658ac85ed88205ccd1ab809899884d (xen-netfront: Fix
handling packets on compound pages with skb_linearize) attempted to
fix a problem where an skb that would have required too many slots
would be dropped causing TCP connections to stall.

However, it filled in the first slot using the original buffer and not
the new one and would use the wrong offset and grant access to the
wrong page.

Netback would notice the malformed request and stop all traffic on the
VIF, reporting:

    vif vif-3-0 vif3.0: txreq.offset: 85e, size: 4002, end: 6144
    vif vif-3-0 vif3.0: fatal error; disabling device

Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
---
 drivers/net/xen-netfront.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index ece8d18..eeed0ce 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -627,6 +627,9 @@ static int xennet_start_xmit(struct sk_buff *skb,
struct net_device *dev)
                                    slots, skb->len);
                if (skb_linearize(skb))
                        goto drop;
+               data = skb->data;
+               offset = offset_in_page(data);
+               len = skb_headlen(skb);
        }

        spin_lock_irqsave(&queue->tx_lock, flags);
-- 
1.7.10.4


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