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Re: [libvirt] [PATCH] do not unref obj in qemuDomainObjExitMonitorWithDriver



On Wed, Mar 16, 2011 at 05:01:23PM +0800, Wen Congyang wrote:
> Steps to reproduce this bug:
> # cat test.sh 
>   #! /bin/bash -x
>   virsh start domain
>   sleep 5
>   virsh qemu-monitor-command domain 'cpu_set 2 online' --hmp
> # while true; do ./test.sh ; done
> 
> Then libvirtd will crash.
> 
> The reason is that:
> we add a reference of obj when we open the monitor. We will reduce this
> reference when we free the monitor.
> 
> If the reference of monitor is 0, we will free monitor automatically and
> the reference of obj is reduced.
> 
> But in the function qemuDomainObjExitMonitorWithDriver(), we reduce this
> reference again when the reference of monitor is 0.
> 
> It will cause the obj be freed in the function qemuDomainObjEndJob().
> 
> Then we start the domain again, and libvirtd will crash in the function
> virDomainObjListSearchName(), because we pass a null pointer(obj->def->name)
> to strcmp().
> 
> Signed-off-by: Wen Congyang <wency cn fujitsu com>
> 
> ---
>  src/qemu/qemu_domain.c |    1 -
>  1 files changed, 0 insertions(+), 1 deletions(-)
> 
> diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
> index 8a2b9cc..ae28b1c 100644
> --- a/src/qemu/qemu_domain.c
> +++ b/src/qemu/qemu_domain.c
> @@ -634,7 +634,6 @@ void qemuDomainObjExitMonitorWithDriver(struct qemud_driver *driver,
>      virDomainObjLock(obj);
>  
>      if (refs == 0) {
> -        virDomainObjUnref(obj);
>          priv->mon = NULL;
>      }
>  }

ACK,  ExitMonitorWithDriver should not be touching the virDomainObjPtr
refs at all. The virDomainObjPtr refs should only be touched by the
BeginJob/EndJob calls.

This same fix also needs to be done in qemuDomainObjExitMonitor()


Daniel
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