Re: [Qemu-ppc] [PATCH] spapr: fix memory hotplug error path

[Greg Kurz]

On Tue, 4 Jul 2017 14:41:33 +0530
Bharata B Rao <address@hidden> wrote:

> On Tue, Jul 04, 2017 at 10:02:46AM +0200, Greg Kurz wrote:
> > > > There is some history to this. I was doing error recovery and 
> > > > propagation
> > > > here similarly during memory hotplug development phase until Igor
> > > > suggested that we shoudn't try to recover after we have done guest
> > > > visible changes.
> > > > 
> > > > Refer to "changes in v6" section in this post:
> > > > https://lists.gnu.org/archive/html/qemu-ppc/2015-06/msg00296.html
> > > > 
> > > > However at that time we were doing memory add by DRC index method
> > > > and hence would attach and online one LMB at a time.
> > > > In that method, if an intermediate attach fails we would end up with a 
> > > > few
> > > > LMBs being onlined by the guest already. However subsequently
> > > > we have switched (optionally, based on dedicated_hp_event_source) to
> > > > count-indexed method of hotplug where we do attach of all LMBs one by 
> > > > one
> > > > and then request the guest to hotplug all of them at once using 
> > > > count-indexed
> > > > method.
> > > > 
> > > > So it will be a bit tricky to abort for index based case and recover
> > > > correctly for count-indexed case.    
> > > 
> > > Looked at the code again and realized that though we started with
> > > index based LMB addition, we later switched to count based addition. Then
> > > we added support for count-indexed type subject to the presence
> > > of dedidated hotplug event source while still retaining the support
> > > for count based addition.
> > > 
> > > So presently we do attach of all LMBs one by one and then do onlining
> > > (count based or count-indexed based) once. Hence error recovery
> > > for both cases would be similar now. So I guess you should take care of
> > > undoing pc_dimm_memory_plug() like Igor mentioned and also undo the
> > > effects of partial successful attaches.
> > >   
> > 
> > I've sent a v2 that adds rollback.  
> 
> oh ok, somehow v2 didn't reach me at all and I saw the v2 in archives only
> now. So just noting that my above replies were sent w/o being aware of v2 :)
> 

No problem at all. It confirms that v2 was indeed needed. Also, it exposes
some details I wasn't aware of. Thanks for the explanation! :)

Cheers,

--
Greg

> > > > 
> > > > Regards,
> > > > Bharata.    
>

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