Re: [dpdk-dev] [PATCH v2] virtio: fix segfault when transmit pkts

["Xie, Huawei" <huawei.xie@intel.com>]

On 4/25/2016 10:37 AM, Tan, Jianfeng wrote:
> Issue: when using virtio nic to transmit pkts, it causes segment fault.
>
> How to reproduce:
> Basically, we need to construct a case with vm send packets to vhost-user,
> and this issue does not happen when transmitting packets using indirect
> desc. Besides, make sure all descriptors are exhausted before vhost
> dequeues any packets.
>
> a. start testpmd with vhost.
>   $ testpmd -c 0x3 -n 4 --socket-mem 1024,0 --no-pci \
>     --vdev 'eth_vhost0,iface=/tmp/sock0,queues=1' -- -i --nb-cores=1
>
> b. start a qemu with a virtio nic connected with the vhost-user port, just
> make sure mrg_rxbuf is enabled.
>
> c. enable testpmd on the host.
>   testpmd> set fwd io
>   testpmd> start (better without start vhost-user)
>
> d. start testpmd in VM.
>   $testpmd -c 0x3 -n 4 -m 1024 -- -i --disable-hw-vlan-filter --txqflags=0xf01
>   testpmd> set fwd txonly
>   testpmd> start
>
> How to fix: this bug is because inside virtqueue_enqueue_xmit(), the flag of
> desc has been updated inside the do {} while (), not necessary to update after
> the loop. (And if we do that after the loop, if all descs could have run out,
> idx is VQ_RING_DESC_CHAIN_END (32768), use this idx to reference the start_dp
> array will lead to segment fault.)
>
> Fixes: dd856dfcb9e ("virtio: use any layout on Tx")
>
> Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
> ---
>  v2: refine the commit message.
>
>  drivers/net/virtio/virtio_rxtx.c | 2 --
>  1 file changed, 2 deletions(-)
>
> diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
> index ef21d8e..432aeab 100644
> --- a/drivers/net/virtio/virtio_rxtx.c
> +++ b/drivers/net/virtio/virtio_rxtx.c
> @@ -271,8 +271,6 @@ virtqueue_enqueue_xmit(struct virtqueue *txvq, struct rte_mbuf *cookie,
>  		idx = start_dp[idx].next;
>  	} while ((cookie = cookie->next) != NULL);
>  
> -	start_dp[idx].flags &= ~VRING_DESC_F_NEXT;
> -
>  	if (use_indirect)
>  		idx = txvq->vq_ring.desc[head_idx].next;
>  

Ack the code.

Acked-by: Huawei Xie <huawei.xie@intel.com>