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Re: [libvirt] [PATCH] virBitmapFree: Change the function to a macro



On Tue, Sep 10, 2013 at 01:29:40AM +0000, Liuji (Jeremy) wrote:
> > -----Original Message-----
> > From: Daniel P. Berrange [mailto:berrange redhat com]
> > Sent: Monday, September 09, 2013 7:26 PM
> > To: Liuji (Jeremy)
> > Cc: libvir-list redhat com; Jinbo (Justin); Luohao (brian); Haofeng
> > Subject: Re: [libvirt] [PATCH] virBitmapFree: Change the function to a macro
> > 
> > On Mon, Sep 09, 2013 at 01:39:42AM +0000, Liuji (Jeremy) wrote:
> > > > -----Original Message-----
> > > > From: Daniel P. Berrange [mailto:berrange redhat com]
> > > > Sent: Friday, September 06, 2013 6:37 PM
> > > > To: Liuji (Jeremy)
> > > > Cc: libvir-list redhat com; Jinbo (Justin); Luohao (brian); Haofeng
> > > > Subject: Re: [libvirt] [PATCH] virBitmapFree: Change the function to a macro
> > > >
> > > > On Fri, Sep 06, 2013 at 10:30:56AM +0000, Liuji (Jeremy) wrote:
> > > > > The parameter of virBitmapFree function is just a pointer, not a pointer of
> > > > pointer.
> > > > > The second VIR_FREE on virBitmapFree only assign NULL to the formal
> > > > parameter.
> > > > > After calling the virBitmapFree function, the actual parameter are still not
> > > > NULL.
> > > > > There are many code segment don't assign NULL to the formal parameter
> > > > after calling
> > > > > the virBitmapFree function. This will bring potential risks.
> > > > >
> > > > > A problem scenario:
> > > > > 1) The XML of VM contain the below segment:
> > > > >     <numatune>
> > > > >         <memory mode='preferred' placement='auto' nodeset='0'/>
> > > > >     </numatune>
> > > > > 2)virsh create the VM
> > > > > 3)In the virDomainDefParseXML funtion:
> > > > >                     /* Ignore 'nodeset' if 'placement' is 'auto' finally
> > */
> > > > >                     if (placement_mode ==
> > > > VIR_NUMA_TUNE_MEM_PLACEMENT_MODE_AUTO) {
> > > > >
> > > > virBitmapFree(def->numatune.memory.nodemask);
> > > > >                         def->numatune.memory.nodemask = NULL;
> > > > >                     }
> > > > > 4)Then, virsh destroy the VM. In the virDomainDefFree funtion, it also call
> > the
> > > > > virBitmapFree function to free the nodemask:
> > > > >     virBitmapFree(def->numatune.memory.nodemask);
> > > > > But after this call, the value of def->numatune.memory.nodemask is still
> > not
> > > > NULL.
> > > > > This will generate an exception.
> > > >
> > > > Have you got an actual crash happening today, or is this just a theoretical
> > > > problem you're trying to address ?
> > >
> > > Yes´╝îit's an actual crash problem. I found the problem in the above problem
> > scenario in my first mail.
> > 
> > Then can you send a patch which explicitly fixes that problem on its
> > own, without doing this major refactoring, which obscures what is being
> > fixed.
> 
> I had sent a patch in my first mail. You can find the mail at the following links:
> https://www.redhat.com/archives/libvir-list/2013-September/msg00337.html

No, I want the root cause fixed. This change to the bitmap APIs is just
papering over any root cause bug.


Daniel
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