Xen devel - Mar 2008 - [PATCH] [Xend] Grab common lock during domain restore op and security op

I am introducing a lock in the path of the domain restore operation.
This lock is acquired when a domain is restored or migrated into a
system. The lock is also acquired during policy operation, i.e., setting
of a domain''s label, which prevents changes to the policy during
restore
operations.

Signed-off-by: Stefan Berger <stefanb@us.ibm.com>



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It seems odd to me that of all update operations that can be performed on a
domain by xend, only label-setting needs explicit serialisation against
domain restore. What''s the underlying problem that this is solving?

 -- Keir

On 10/3/08 21:59, "Stefan Berger" <stefanb@us.ibm.com> wrote:
> I am introducing a lock in the path of the domain restore operation.
> This lock is acquired when a domain is restored or migrated into a
> system. The lock is also acquired during policy operation, i.e., setting
> of a domain''s label, which prevents changes to the policy during
restore
> operations.
> 
> Signed-off-by: Stefan Berger <stefanb@us.ibm.com>
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel


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xen-devel-bounces@lists.xensource.com wrote on 03/10/2008 06:06:38 PM:
> It seems odd to me that of all update operations that can be performed 
on a
> domain by xend, only label-setting needs explicit serialisation against
> domain restore. What''s the underlying problem that this is
solving?
If it''s not serialized, one could otherwise change the policy while a 
migration is happening. In the worst case this would lead to the new VM 
running on a system that it otherwise would not be allowed to run (due to 
the modified policy). I would have grabbed the domains_lock lock 
otherwise, but then I found this here in the XendCheckpoint.restore() 
method which is called with the domains_lock() held:


        #
        # We shouldn''t hold the domains_lock over a waitForDevices
        # As this function sometime gets called holding this lock,
        # we must release it and re-acquire it appropriately
        #
        from xen.xend import XendDomain

        lock = True;
        try:
            XendDomain.instance().domains_lock.release()
        except:
            lock = False;

        try:
            dominfo.waitForDevices() # Wait for backends to set up
        except Exception, exn:
            log.exception(exn)

        if lock:
            XendDomain.instance().domains_lock.acquire()


To me it looks like introducing another lock is necessary.

   Stefan

> 
>  -- Keir
> 
> On 10/3/08 21:59, "Stefan Berger" <stefanb@us.ibm.com>
wrote:
> 
> > I am introducing a lock in the path of the domain restore operation.
> > This lock is acquired when a domain is restored or migrated into a
> > system. The lock is also acquired during policy operation, i.e., 
setting
> > of a domain''s label, which prevents changes to the policy
during
restore
> > operations.
> > 
> > Signed-off-by: Stefan Berger <stefanb@us.ibm.com>
> > 
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@lists.xensource.com
> > http://lists.xensource.com/xen-devel
> 
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel

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