Hi Stephen, On 4/26/2016 12:48 PM, Stephen Hemminger wrote: > On Thu, 21 Apr 2016 12:36:10 +0000 > Jianfeng Tan <jianfeng.tan at intel.com> wrote: > >> Issue: when using virtio nic to transmit pkts, it causes segment fault. >> >> How to reproduce: >> 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. >> $qemu -smp cores=2,sockets=1 -cpu host -enable-kvm vm-0.img -vnc :5 -m 4G \ >> -object memory-backend-file,id=mem,size=4096M,mem-path=<path>,share=on \ >> -numa node,memdev=mem -mem-prealloc \ >> -chardev socket,id=char1,path=$sock_vhost \ >> -netdev type=vhost-user,id=net1,chardev=char1 \ >> -device virtio-net-pci,netdev=net1,mac=00:01:02:03:04:05 >> c. enable testpmd on the host. >> testpmd> set fwd io >> testpmd> start >> 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 (); and after the loop, all >> descs >> could have run out, so idx is VQ_RING_DESC_CHAIN_END (32768), use this idx to >> reference the start_dp array will lead to segment fault. >> >> Signed-off-by: Jianfeng Tan <jianfeng.tan at intel.com> >> --- >> 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; >> > At this point in the code idx is the index past the current set of ring > descriptors. So yes this is a real bug. > > I think the description meta-data needs work to explain it better. > > Yes, please see v2. Yuanhan gives a hand to refine it already.
Thanks, Jianfeng