This bug was initially created as a copy of Bug #1880299

I am copying this bug because: 



Description of problem:
Boot VM with vhost-user 4 queues, then boot testpmd as vhost-user client. Kill testpmd and start testpmd again, vhost-user connection fails to restart. This will cause both qemu and testpmd crash.

Version-Release number of selected component (if applicable):
4.18.0-237.el8.x86_64
qemu-kvm-5.1.0-7.module+el8.3.0+8099+dba2fe3e.x86_64
dpdk-19.11.3-1.el8.x86_64

How reproducible:
100%

Steps to Reproduce:
1. Boot VM with vhost-user 4 queues 

    <interface type="vhostuser">
      <mac address="88:66:da:5f:dd:02" />
      <source mode="server" path="/tmp/vhost-user1.sock" type="unix" />
      <model type="virtio" />
      <driver ats="on" iommu="on" name="vhost" queues="4" rx_queue_size="1024" />
      <address bus="0x6" domain="0x0000" function="0x0" slot="0x00" type="pci" />
    </interface>



2. Boot testpmd as vhost-user client

# cat testpmd_4q.sh 
testpmd \
-l 2,4,6,8,10,12,14,16,18 \
--socket-mem 1024,1024 \
-n 4  \
--vdev 'net_vhost0,iface=/tmp/vhost-user1.sock,queues=4,client=1,iommu-support=1' \
-d /usr/lib64/librte_pmd_vhost.so \
-- \
--portmask=f \
-i \
--rxd=512 --txd=512 \
--rxq=4 --txq=4 \
--nb-cores=8 \
--forward-mode=txonly

# sh testpmd_4q.sh 

3. Kill testpmd

# pkill testpmd


4. Start testpmd again

# sh testpmd.sh

5. vhost-user connection fails to restart. Both qemu and testpmd crash.

testpmd_4q.sh: line 13:  5227 Segmentation fault      (core dumped) testpmd -l 2,4,6,8,10,12,14,16,18 --socket-mem 1024,1024 -n 4 --vdev 'net_vhost0,iface=/tmp/vhost-user1.sock,queues=4,client=1,iommu-support=1' -d /usr/lib64/librte_pmd_vhost.so -- --portmask=f -i --rxd=512 --txd=512 --rxq=4 --txq=4 --nb-cores=8 --forward-mode=txonly

# dmesg
[ 3782.630934] vhost-events[5239]: segfault at 2d8 ip 00007f5dc8e171cb sp 00007f5db97f9870 error 4 in librte_vhost.so.20.0[7f5dc8e10000+4e000]
[ 3782.643491] Code: 89 40 08 e9 3f ff ff ff e8 22 bc ff ff 66 90 f3 0f 1e fa 41 57 41 56 41 55 41 54 49 89 cc 55 48 89 f5 53 48 89 fb 48 83 ec 48 <4c> 8b af d8 02 00 00 48 89 14 24 44 89 44 24 10 64 48 8b 04 25 28
[ 3784.517001] qemu-kvm[5097]: segfault at 1b0 ip 000055b8b3406540 sp 00007ffded2577f0 error 4 in qemu-kvm[55b8b304d000+a66000]
[ 3784.528225] Code: 75 10 48 8b 05 71 80 ae 00 89 c0 64 48 89 03 0f ae f0 90 48 8b 45 00 31 c9 85 d2 48 89 e7 0f 95 c1 41 b8 01 00 00 00 4c 89 e2 <48> 8b b0 b0 01 00 00 e8 64 d2 f5 ff 48 83 3c 24 00 0f 84 f9 00 00


Actual results:
vhost-user connection fails to restart. Both qemu and testpmd crash.

Expected results:
vhost-user connection should restart well. And qemu and testpmd should work well.

Additional info:
1. This issue can not be reproduced with vhost-user 2 queues. We need to test with vhost-user 4 queues to trigger.