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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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      Last update: 2010-09-01 12:53    [W:0.022 / U:37.232 seconds]
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