[Qemu-devel] [Bug 1019179] [NEW] vCPU hot-add makes the guest abort

[Yongjie Ren]

Public bug reported:

Environment:
------------
Host OS (ia32/ia32e/IA64):ia32e
Guest OS (ia32/ia32e/IA64):ia32e
Guest OS Type (Linux/Windows):Linux(RHEL6u1)
kvm.git Commit:ae7a2a3fb6f8b784c2752863f4f1f20c656f76fb
qemu-kvm Commit:a212f79fc4596570124fb864425b980c157cd001
Host Kernel Version:3.5.0-rc1
Hardware:Romley-EP, WSM-EP


Bug detailed description:
--------------------------
Hot-add vcpu for a guest in qemu monitor will make the guest abort. (QEMU 
process is killed.)
After Hot-removing vcpu for the guest in qemu monitor, the guest will be still 
alive but the the number of vCPU in the guest doesn't decrease.

Reproduce steps:
----------------
Hot-add vCPU:
1.start up a host with kvm (commit: ae7a2a3f)and qemu-kvm(commit: a212f79f..)
2.qemu-system-x86_64 -m 1024 -smp 4,maxvcpus=10 –hda /root/rhel6u3.qcow
3. ls /sys/devices/system/cpu/    (to check CPUs in guest)
4. ctrl+alt+2      (swith to qemu monitor)
5. cpu_set 5 online

Hot-remove vCPU:
1.start up a host with kvm (commit: ae7a2a3f) and qemu-kvm(commit: a212f79f..)
2.qemu-system-x86_64 -m 1024 -smp 4,maxvcpus=10 –hda /root/rhel6u3.qcow
3. ls /sys/devices/system/cpu/        (to check CPUs in guest)
4. ctrl+alt+2   (swith to qemu monitor)
5. cpu_set 2 offline
6. ctrl+alt+1
7. ls /sys/devices/system/cpu/            (to check CPUs in guest)

Current result:
----------------
vCPU hot-add will cause guest abort.
vCPU hot-remove doesn't decrease the number of vCPU in guest.

Expected result:
----------------
The number of the  guest’s cpu changes as we expect.

Basic root-causing log:
----------------------
address@hidden ~]# qemu-system-x86_64 -m 1024 -smp 4,maxcpus=10 -hda
/root/rhel6u3.qcow 
VNC server running on `::1:5900'
qemu-system-x86_64: hw/qdev.c:84: qdev_set_parent_bus: Assertion
`bus->allow_hotplug' failed.
Aborted (core dumped)

** Affects: qemu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1019179

Title:
  vCPU hot-add makes the guest abort

Status in QEMU:
  New

Bug description:
  Environment:
  ------------
  Host OS (ia32/ia32e/IA64):ia32e
  Guest OS (ia32/ia32e/IA64):ia32e
  Guest OS Type (Linux/Windows):Linux(RHEL6u1)
  kvm.git Commit:ae7a2a3fb6f8b784c2752863f4f1f20c656f76fb
  qemu-kvm Commit:a212f79fc4596570124fb864425b980c157cd001
  Host Kernel Version:3.5.0-rc1
  Hardware:Romley-EP, WSM-EP

  
  Bug detailed description:
  --------------------------
  Hot-add vcpu for a guest in qemu monitor will make the guest abort. (QEMU 
process is killed.)
  After Hot-removing vcpu for the guest in qemu monitor, the guest will be 
still alive but the the number of vCPU in the guest doesn't decrease.

  Reproduce steps:
  ----------------
  Hot-add vCPU:
  1.start up a host with kvm (commit: ae7a2a3f)and qemu-kvm(commit: a212f79f..)
  2.qemu-system-x86_64 -m 1024 -smp 4,maxvcpus=10 –hda /root/rhel6u3.qcow
  3. ls /sys/devices/system/cpu/    (to check CPUs in guest)
  4. ctrl+alt+2      (swith to qemu monitor)
  5. cpu_set 5 online

  Hot-remove vCPU:
  1.start up a host with kvm (commit: ae7a2a3f) and qemu-kvm(commit: a212f79f..)
  2.qemu-system-x86_64 -m 1024 -smp 4,maxvcpus=10 –hda /root/rhel6u3.qcow
  3. ls /sys/devices/system/cpu/        (to check CPUs in guest)
  4. ctrl+alt+2   (swith to qemu monitor)
  5. cpu_set 2 offline
  6. ctrl+alt+1
  7. ls /sys/devices/system/cpu/            (to check CPUs in guest)

  Current result:
  ----------------
  vCPU hot-add will cause guest abort.
  vCPU hot-remove doesn't decrease the number of vCPU in guest.

  Expected result:
  ----------------
  The number of the  guest’s cpu changes as we expect.

  Basic root-causing log:
  ----------------------
  address@hidden ~]# qemu-system-x86_64 -m 1024 -smp 4,maxcpus=10 -hda
  /root/rhel6u3.qcow 
  VNC server running on `::1:5900'
  qemu-system-x86_64: hw/qdev.c:84: qdev_set_parent_bus: Assertion
  `bus->allow_hotplug' failed.
  Aborted (core dumped)

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