Description of problem:
Failed to start domain due to "Spice-ERROR **: reds.c:3975:do_spice_init: statistics shm_open failed, Permission denied"

Version-Release number of selected component (if applicable):
libvirt-1.2.8-10.el7.x86_64
spice-server-0.12.4-8.el7.x86_64
qemu-kvm-rhev-2.1.2-16.el7.x86_64

How reproducible:
low(<10%)

Steps to Reproduce:
[root@ibm-x3850x5-02 images]# cat /etc/libvirt/libvirtd.conf | grep "^[^#]"
listen_tcp = 1
auth_tcp = "none"
auth_tls = "none"
max_anonymous_clients = 20000
max_workers = 20000
max_requests = 20000
max_client_requests = 5000
log_level = 1
log_outputs="1:file:/var/log/libvirt/libvirtd.log" 
log_filters="1:qemu 1:libvirt 1:conf 1:json"
[root@ibm-x3850x5-02 images]# cat /etc/libvirt/qemu.conf | grep "^[^#]"
max_processes = 1000000
max_files = 1000000
[root@ibm-x3850x5-02 images]# cat /etc/systemd/system/multi-user.target.wants/libvirtd.service| grep Limit
LimitNOFILE=2048000
[root@ibm-x3850x5-02 images]# 

[root@dhcp-66-83-39 testing]# for i in `seq 1 1024`; do qemu-img create -f qcow2 guest$i.img 1M; done

[root@ibm-x3850x5-02 scalability]# cat define.sh 
#! /bin/sh -

for i in `seq 1 1024`
do
sed -i "s,#num#,guest$i,g" r7.xml
virsh define r7.xml
sed -i "s,guest$i,#num#,g" r7.xml
#sleep 1
done

[root@ibm-x3850x5-02 scalability]# for i in {1..1024};do virsh start guest$i;done
...
Domain guest569 started

error: Failed to start domain guest570
error: internal error: process exited while connecting to monitor: ((null):13809): Spice-ERROR **: reds.c:3975:do_spice_init: statistics shm_open failed, Permission denied


Domain guest571 started

Domain guest572 started

Domain guest573 started

Domain guest574 started

error: Failed to start domain guest575
error: internal error: early end of file from monitor: possible problem:
((null):13872): Spice-ERROR **: reds.c:3975:do_spice_init: statistics shm_open failed, Permission denied


Domain guest576 started

Domain guest577 started

Domain guest578 started

Domain guest579 started

Domain guest580 started

Domain guest581 started

Domain guest582 started
...

Actual results:
As shown above steps, start 1024 domains, hit this issue 28 times. Try to start it again, the failed domain can be started successfully. 
[root@ibm-x3850x5-02 scalability]# virsh start guest575
Domain guest575 started

+++++++++++
[root@ibm-x3850x5-02 scalability]# cat /var/log/libvirt/qemu/guest575.log
...
2014-12-26 06:24:32.568+0000: 13872: debug : qemuProcessHook:3083 : Hook complete ret=0
2014-12-26 06:24:32.568+0000: 13872: debug : virExec:691 : Done hook 0
2014-12-26 06:24:32.568+0000: 13872: debug : virExec:698 : Setting child security label to system_u:system_r:svirt_t:s0:c140,c239
2014-12-26 06:24:32.568+0000: 13872: debug : virExec:728 : Setting child uid:gid to 107:107 with caps 0
2014-12-26 06:24:32.569+0000: 13872: debug : virCommandHandshakeChild:431 : Notifying parent for handshake start on 583
2014-12-26 06:24:32.570+0000: 13872: debug : virCommandHandshakeChild:439 : Waiting on parent for handshake complete on 584
2014-12-26 06:24:32.676+0000: 13872: debug : virFileClose:99 : Closed fd 583
2014-12-26 06:24:32.676+0000: 13872: debug : virFileClose:99 : Closed fd 584
2014-12-26 06:24:32.676+0000: 13872: debug : virCommandHandshakeChild:459 : Handshake with parent is done
char device redirected to /dev/pts/548 (label charserial0)
((null):13872): Spice-ERROR **: reds.c:3975:do_spice_init: statistics shm_open failed, Permission denied
2014-12-26 06:24:33.559+0000: shutting down
...
+++++++++++

Expected results:
Start a lot of domain continually, each domain should be started normally.

Additional info:
[root@ibm-x3850x5-02 scalability]# cat r7.xml 
<domain type='kvm'>
  <name>#num#</name>
  <memory unit='M'>128</memory>
  <vcpu placement='static'>4</vcpu>
  <os>
    <type arch='x86_64' machine='pc-i440fx-rhel7.1.0'>hvm</type>
    <boot dev='hd'/>
  </os>
  <features>
    <acpi/>
    <apic/>
    <pae/>
  </features>
  <clock offset='utc'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <devices>
    <emulator>/usr/libexec/qemu-kvm</emulator>
   <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2' cache='none'/>
      <source file='/home/images/#num#.img'/>
      <target dev='hda' bus='ide'/>
    </disk>
    <controller type='pci' index='0' model='pci-root'/>
    <controller type='virtio-serial' index='0'>
    </controller>
    <serial type='pty'>
      <target port='0'/>
    </serial>
    <console type='pty'>
      <target type='serial' port='0'/>
    </console>
    <channel type='spicevmc'>
      <target type='virtio' name='com.redhat.spice.0'/>
    </channel>
    <input type='tablet' bus='usb'/>
    <input type='mouse' bus='ps2'/>
    <graphics type='spice' autoport='yes'/>
    <video>
      <model type='qxl' ram='65536' vram='65536' heads='1'/>
    </video>
    <memballoon model='none'>
    </memballoon>
  </devices>
</domain>