Hi Yuanhan, > -----Original Message----- > From: Yuanhan Liu [mailto:yuanhan.liu at linux.intel.com] > Sent: Tuesday, April 26, 2016 11:43 AM > To: Tan, Jianfeng > Cc: dev at dpdk.org; Xie, Huawei > Subject: Re: [PATCH v2] virtio: fix segfault when transmit pkts > > On Mon, Apr 25, 2016 at 02:37:45AM +0000, Jianfeng Tan 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. > > That's not a right "because": you were stating a fact of the right way > to do setup desc flags, but not the cause of this bug. > > > (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.) > > And that's the cause. So, you should state the cause first, then the fix > (which we already have), but not in the verse order you just did. > > So, I'd like to reword the commit log a bit, to something like following. > What do you think of it? If no objection, I could merge it soon. Thanks > for the fix, BTW! >
Your refinement sounds much better, thanks! Jianfeng
