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 at 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 at intel.com>
