linux-kernel - Re: linux 3.3-pre-rc1: Starting domU fails with Error: Failed to query current memory allocation of dom0.

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Date:	Thu, 12 Jan 2012 12:10:19 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Sander Eikelenboom <linux@...elenboom.it>
Cc:	Kay Sievers <kay.sievers@...y.org>, linux-kernel@...r.kernel.org,
	xen-devel <xen-devel@...ts.xensource.com>
Subject: Re: linux 3.3-pre-rc1: Starting domU fails with Error: Failed to
 query current memory allocation of dom0.

On Thu, Jan 12, 2012 at 06:05:46PM +0100, Sander Eikelenboom wrote:
> Hello Konrad,
> 
> Thursday, January 12, 2012, 5:40:25 PM, you wrote:
> 
> > On Thu, Jan 12, 2012 at 11:12:04AM -0500, Konrad Rzeszutek Wilk wrote:
> >> On Thu, Jan 12, 2012 at 05:05:34PM +0100, Kay Sievers wrote:
> >> > On Thu, Jan 12, 2012 at 16:46, Konrad Rzeszutek Wilk
> >> > <konrad.wilk@...cle.com> wrote:
> >> > > On Thu, Jan 12, 2012 at 01:38:32PM +0100, Sander Eikelenboom wrote:
> >> > 
> >> > >> Today i tried linuses tree of today (last commit is 4c4d285ad5665bfbd983b95fde8d7a477d24a361).
> >> > >>
> >> > >> It boots dom0 fine, but it fails to start any domU with: "Error: Failed to query current memory allocation of dom0."
> >> > >> With my previous 3.1.5 kernel everything is fine, nothing else changed in config in between.
> >> > > Your patch that converts the xen-balloon to use the regular device bus driver
> >> > > (070680218379e15c1901f4bf21b98e3cbf12b527) has some not-so-happy consequences.
> >> > >
> >> > > The toolstack (xen-tools) use:
> >> > >
> >> > > /sys/devices/system/xen_memory/xen_memory0
> >> > >
> >> > > But with the change, it is now:
> >> > >
> >> > > /sys/devices/xen_memory0/target_kb
> >> > 
> >> > Urks, seems like a mistake on my side.
> >> > 
> >> > Please try if changing:
> >> >   bus_unregister(&balloon_subsys);
> >> > to:
> >> >   subsys_system_register(&balloon_subsys, NULL);
> >> > in:
> >> >   drivers/xen/xen-balloon.c
> >> > fixes the issue.
> >> 
> >> Heh. I was *just* looking at d369a5d8fc70710236ae2d06a0e42dce483712df
> >> ("clocksource: convert sysdev_class to a regular subsystem") and typed up this patch
> >> to try it out:
> 
> > Kay, are you Acking this patch? (I can send it to Linus for rc0 or rc1)
> 
> > commit 4e6f161986678a25c9e76af98df928408c734a27
> > Author: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> > Date:   Thu Jan 12 11:35:50 2012 -0500
> 
> >     xen/balloon: Move the registration from device to subsystem.
> >     
> >     With git commit 070680218379e15c1901f4bf21b98e3cbf12b527
> >     "xen-balloon: convert sysdev_class to a regular subsystem" we would
> >     end up with the attributes being put in:
> >     
> >      /sys/devices/xen_memory0/target_kb
> >     instead of
> >     /sys/devices/system/xen_memory/xen_memory0/target_kb
> >     
> >     Making the tools unable to deflate the kernel to make more space
> >     for launching another guest and printing:
> 
> >     Error: Failed to query current memory allocation of dom0
> >     
> >     Reported-by: Sander Eikelenboom <linux@...elenboom.it>
> >     Suggested-by:  Kay Sievers <kay.sievers@...y.org>
> >     Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> 
> > diff --git a/drivers/xen/xen-balloon.c b/drivers/xen/xen-balloon.c
> > index 3832e30..596e6a7 100644
> > --- a/drivers/xen/xen-balloon.c
> > +++ b/drivers/xen/xen-balloon.c
> > @@ -221,7 +221,7 @@ static int register_balloon(struct device *dev)
> >  {
> >         int i, error;
> >  
> > -       error = bus_register(&balloon_subsys);
> > +       error = subsys_system_register(&balloon_subsys, NULL);
> >         if (error)
> >                 return error;
> >  
> 
> 
> Shouldn't the
> 
> if (error) {
>         bus_unregister(&balloon_subsys);
>         return error;
> }
> 
> right below it also be changed ?

I thought so too, but looking at how the subsys_system_register it looks
to be OK. Kay, thoughts?
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