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SubjectRe: [Bug #16626] Machine hangs with EIP at skb_copy_and_csum_dev
Plamen, could you test following patch ?

I reproduced problem on a dev machine and following patch cured it.


[PATCH] gro: fix different skb headrooms

packets entering GRO might have different headrooms, even for a given
flow (because of implementation details in drivers, like copybreak).
We cant force drivers to deliver packets with a fixed headroom.

1) fix skb_segment()

skb_segment() makes the false assumption headrooms of fragments are same
than the head. When CHECKSUM_PARTIAL is used, this can give csum_start
errors, and crash later in skb_copy_and_csum_dev()

2) allocate a minimal skb for head of frag_list

skb_gro_receive() uses netdev_alloc_skb(headroom + skb_gro_offset(p)) to
allocate a fresh skb. This adds NET_SKB_PAD to a padding already
provided by netdevice, depending on various things, like copybreak.

Use alloc_skb() to allocate an exact padding, to reduce cache line

bugzilla :

Many thanks to Plamen Petrov, testing many debugging patches !
With help of Jarek Poplawski.

Reported-by: Plamen Petrov <>
Signed-off-by: Eric Dumazet <>
CC: Jarek Poplawski <>
patch against linux-2.6 current tree

net/core/skbuff.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 3a2513f..26396ff 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2573,6 +2573,10 @@ struct sk_buff *skb_segment(struct sk_buff *skb, int features)
__copy_skb_header(nskb, skb);
nskb->mac_len = skb->mac_len;

+ /* nskb and skb might have different headroom */
+ if (nskb->ip_summed == CHECKSUM_PARTIAL)
+ nskb->csum_start += skb_headroom(nskb) - headroom;
skb_set_network_header(nskb, skb->mac_len);
nskb->transport_header = (nskb->network_header +
@@ -2702,8 +2706,8 @@ int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb)
} else if (skb_gro_len(p) != pinfo->gso_size)
return -E2BIG;

- headroom = skb_headroom(p);
- nskb = netdev_alloc_skb(p->dev, headroom + skb_gro_offset(p));
+ headroom = NET_SKB_PAD + NET_IP_ALIGN;
+ nskb = alloc_skb(headroom + skb_gro_offset(p), GFP_ATOMIC);
if (unlikely(!nskb))
return -ENOMEM;

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