On Thu, 12 Jun 2014 22:46:14 +0800
Tyrone Lau <tyronelau at gmail.com> wrote:
> Hi, all. I have found recently the Linux kernel will complain occasionally
> a dead lock, while I use the kernel module rte_kni provided in DPDK. After
> reviewing the dpdk source code and googling,
> I found that the deadlock occurred because netif_receive_skb is invoked in
> a non-softirq context. The erroneous source code is listed as below (in
> lib/librte_eal/linuxapp/kni/kni_net.c:kni_net_rx_normal):
>
> * /* Transfer received packets to netif */
> for (i = 0; i < num; i++) {
> kva = (void *)va[i] - kni->mbuf_va + kni->mbuf_kva;
> len = kva->data_len;
> data_kva = kva->data - kni->mbuf_va + kni->mbuf_kva;
>
> skb = dev_alloc_skb(len + 2);
> if (!skb) {
> KNI_ERR("Out of mem, dropping pkts\n");
> /* Update statistics */
> kni->stats.rx_dropped++;
> }
> else {
> /* Align IP on 16B boundary */
> skb_reserve(skb, 2);
> memcpy(skb_put(skb, len), data_kva, len);
> skb->dev = dev;
> skb->protocol = eth_type_trans(skb, dev);
> skb->ip_summed = CHECKSUM_UNNECESSARY;
>
> /* Call netif interface */
> netif_receive_skb(skb);
>
> /* Update statistics */
> kni->stats.rx_bytes += len;
> kni->stats.rx_packets++;
> }
> }*
>
> The similar bug is reported and fixed in dpdk extension memnic. See
>
> http://comments.gmane.org/gmane.comp.networking.dpdk.devel/3151
>
> To fix this bug, we should call local_bh_disable/local_bh_enable
> around netif_receive_skb to disable and re-enable soft-irq.
> Best Regards
Probably better to call netif_rx instead, because that will
handle the case of overrun.
Other comments, this code should be using per-cpu stats.
it should use netdev_alloc_skb_ip_align rather than doing align itself.
Even better yet would be bursting packets into the receive handler.
