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    SubjectRe: [PATCH net 4/9] virtio-net: correctly handle XDP_PASS for linearized packets
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    On 2016年12月23日 23:57, John Fastabend wrote:
    > On 16-12-23 06:37 AM, Jason Wang wrote:
    >> When XDP_PASS were determined for linearized packets, we try to get
    >> new buffers in the virtqueue and build skbs from them. This is wrong,
    >> we should create skbs based on existed buffers instead. Fixing them by
    >> creating skb based on xdp_page.
    >>
    >> With this patch "ping 192.168.100.4 -s 3900 -M do" works for XDP_PASS.
    >>
    >> Cc: John Fastabend <john.r.fastabend@intel.com>
    >> Signed-off-by: Jason Wang <jasowang@redhat.com>
    >> ---
    >> drivers/net/virtio_net.c | 10 ++++++++--
    >> 1 file changed, 8 insertions(+), 2 deletions(-)
    >>
    >> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
    >> index 58ad40e..470293e 100644
    >> --- a/drivers/net/virtio_net.c
    >> +++ b/drivers/net/virtio_net.c
    >> @@ -578,8 +578,14 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
    >> act = do_xdp_prog(vi, rq, xdp_prog, xdp_page, offset, len);
    >> switch (act) {
    >> case XDP_PASS:
    >> - if (unlikely(xdp_page != page))
    >> - __free_pages(xdp_page, 0);
    >> + /* We can only create skb based on xdp_page. */
    >> + if (unlikely(xdp_page != page)) {
    >> + rcu_read_unlock();
    >> + put_page(page);
    >> + head_skb = page_to_skb(vi, rq, xdp_page,
    >> + 0, len, PAGE_SIZE);
    >> + return head_skb;
    >> + }
    >> break;
    >> case XDP_TX:
    >> if (unlikely(xdp_page != page))
    >>
    > Great thanks. This was likely working before because of the memory
    > leak fixed in 3/9.

    Looks not, without this and 3/9 the code will try to get buffers and
    build skb for a new packet instead of existed buffers.

    Thanks

    >
    > Acked-by: John Fastabend <john.r.fastabend@intel.com>

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