[Xen-devel] xennet: skb rides the rocket: 20 slots

[Sander Eikelenboom <linux@xxxxxxxxxxxxxx>]

Hi Ian,

Today i fired up an old VM with a bittorrent client, trying to download some 
torrents.
I seem to be hitting the unlikely case of "xennet: skb rides the rocket: xx 
slots" and this results in some dropped packets in domU, I don't see any 
warnings in dom0.

I have added some extra info, but i don't have enough knowledge if this 
could/should be prevented from happening ?

[16798.629141] xennet: skb rides the rocket: 19 slots MAX_SKB_FRAGS: 17 
div_roundup:1 xennet_count_skb_frag_slots:18 offset:106 skb_headlen:1622 
skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:4 
page_size:4096 prot:0800
[16800.575182] xennet: skb rides the rocket: 19 slots MAX_SKB_FRAGS: 17 
div_roundup:1 xennet_count_skb_frag_slots:18 offset:2154 skb_headlen:1622 
skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:4 
page_size:4096 prot:0800
[16801.589166] xennet: skb rides the rocket: 20 slots MAX_SKB_FRAGS: 17 
div_roundup:1 xennet_count_skb_frag_slots:19 offset:2154 skb_headlen:1622 
skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:5 
page_size:4096 prot:0800
[16803.279039] xennet: skb rides the rocket: 19 slots MAX_SKB_FRAGS: 17 
div_roundup:1 xennet_count_skb_frag_slots:18 offset:106 skb_headlen:1622 
skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:3 
page_size:4096 prot:0800
[16809.973268] xennet: skb rides the rocket: 19 slots MAX_SKB_FRAGS: 17 
div_roundup:1 xennet_count_skb_frag_slots:18 offset:2154 skb_headlen:1622 
skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:4 
page_size:4096 prot:0800
[16811.420048] xennet: skb rides the rocket: 19 slots MAX_SKB_FRAGS: 17 
div_roundup:1 xennet_count_skb_frag_slots:18 offset:2154 skb_headlen:1622 
skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:6 
page_size:4096 prot:0800
[16814.872686] xennet: skb rides the rocket: 19 slots MAX_SKB_FRAGS: 17 
div_roundup:1 xennet_count_skb_frag_slots:18 offset:106 skb_headlen:1622 
skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:5 
page_size:4096 prot:0800
[16815.359099] xennet: skb rides the rocket: 21 slots MAX_SKB_FRAGS: 17 
div_roundup:1 xennet_count_skb_frag_slots:20 offset:2154 skb_headlen:1622 
skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:5 
page_size:4096 prot:0800
[16825.851906] xennet: skb rides the rocket: 20 slots MAX_SKB_FRAGS: 17 
div_roundup:1 xennet_count_skb_frag_slots:19 offset:106 skb_headlen:1622 
skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:4 
page_size:4096 prot:0800
[16828.295083] xennet: skb rides the rocket: 19 slots MAX_SKB_FRAGS: 17 
div_roundup:1 xennet_count_skb_frag_slots:18 offset:2154 skb_headlen:1622 
skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:5 
page_size:4096 prot:0800
[16837.386684] xennet: skb rides the rocket: 19 slots MAX_SKB_FRAGS: 17 
div_roundup:1 xennet_count_skb_frag_slots:18 offset:106 skb_headlen:1622 
skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:4 
page_size:4096 prot:0800
[16838.609683] xennet: skb rides the rocket: 20 slots MAX_SKB_FRAGS: 17 
div_roundup:1 xennet_count_skb_frag_slots:19 offset:106 skb_headlen:1622 
skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:4 
page_size:4096 prot:0800
[16841.783729] xennet: skb rides the rocket: 19 slots MAX_SKB_FRAGS: 17 
div_roundup:1 xennet_count_skb_frag_slots:18 offset:106 skb_headlen:1622 
skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:6 
page_size:4096 prot:0800
[16843.841678] xennet: skb rides the rocket: 20 slots MAX_SKB_FRAGS: 17 
div_roundup:1 xennet_count_skb_frag_slots:19 offset:2154 skb_headlen:1622 
skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:4 
page_size:4096 prot:0800
[16849.847614] xennet: skb rides the rocket: 19 slots MAX_SKB_FRAGS: 17 
div_roundup:1 xennet_count_skb_frag_slots:18 offset:3690 skb_headlen:54 
skb->len:64294, skb->data_len:64240 skb->truesize:65008 nr_frags:4 
page_size:4096 prot:0800
[16853.787128] xennet: skb rides the rocket: 20 slots MAX_SKB_FRAGS: 17 
div_roundup:1 xennet_count_skb_frag_slots:19 offset:2154 skb_headlen:1622 
skb->len:64294, skb->data_len:62672 skb->truesize:64976 nr_frags:4 
page_size:4096 prot:0800

# ifconfig
eth0      Link encap:Ethernet  HWaddr 00:16:3e:c4:20:46
          inet addr:192.168.1.12  Bcast:192.168.1.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:9090214 errors:0 dropped:0 overruns:0 frame:0
          TX packets:5902090 errors:0 dropped:304 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:19757934770 (18.4 GiB)  TX bytes:16855238200 (15.6 GiB)
          Interrupt:25




diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index c26e28b..50ac403 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -552,7 +552,11 @@ static int xennet_start_xmit(struct sk_buff *skb, struct 
net_device *dev)
                xennet_count_skb_frag_slots(skb);
        if (unlikely(slots > MAX_SKB_FRAGS + 1)) {
                net_alert_ratelimited(
-                       "xennet: skb rides the rocket: %d slots\n", slots);
+                       "xennet: skb rides the rocket: %d slots MAX_SKB_FRAGS: 
%d div_roundup:%d xennet_count_skb_frag_slots:%d offset:%d skb_headlen:%d 
skb->len:%d, skb->data_len:%d skb->truesize:%d nr_frags:%d page_size:%d 
prot:%04x \n
+                             slots, MAX_SKB_FRAGS,DIV_ROUND_UP(offset + len, 
PAGE_SIZE),
+                             xennet_count_skb_frag_slots(skb), offset, len, 
skb->len,
+                             skb->data_len, skb->truesize, 
skb_shinfo(skb)->nr_frags,
+                             PAGE_SIZE, ntohs(skb->protocol));
                goto drop;
        }


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