[dpdk-dev] A deadlock may occur in kni kernel thread while netif_receive_skb is called

[Tyrone Lau <tyronelau@gmail.com>]

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