Re: [Xen-devel] [PATCH] xen-pt: Fix PCI devices re-attach failed

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Stefano Stabellini
> Sent: Monday, January 12, 2015 7:36 PM
> 
> On Wed, 24 Dec 2014, Liang Li wrote:
> > Use the 'xl pci-attach $DomU $BDF' command to attach more then
> > one PCI devices to the guest, then detach the devices with
> > 'xl pci-detach $DomU $BDF', after that, re-attach these PCI
> > devices again, an error message will be reported like following:
> >
> > libxl: error: libxl_qmp.c:287:qmp_handle_error_response: receive
> > an error message from QMP server: Duplicate ID 'pci-pt-03_10.1'
> > for device.
> >
> > The count of calling xen_pt_region_add and xen_pt_region_del are
> > not the same will cause the XenPCIPassthroughState and it's related
> > QemuOpts object not be released properly.
> 
> Thanks for the patch!
> 
> From this description, I don't quite understand why the
> memory_region_ref and memory_region_unref calls are wrong.  What do
> you
> mean by "The count of calling xen_pt_region_add and xen_pt_region_del
> are not the same"?
> 
> On unplug xen_pt_region_del does not get called?
> Or the memory region argument is not exactly the same as the one
> initially passed to xen_pt_region_add?
> 

agree. Liang, could you elaborate how the patch is associated with above 
explanation? :-)

> 
> > Signed-off-by: Liang Li <liang.z.li@xxxxxxxxx>
> > Reported-by: Longtao Pang <longtaox.pang@xxxxxxxxx>
> > ---
> >  hw/xen/xen_pt.c | 4 ----
> >  1 file changed, 4 deletions(-)
> >
> > diff --git a/hw/xen/xen_pt.c b/hw/xen/xen_pt.c
> > index c1bf357..523b8a2 100644
> > --- a/hw/xen/xen_pt.c
> > +++ b/hw/xen/xen_pt.c
> > @@ -588,7 +588,6 @@ static void xen_pt_region_add(MemoryListener *l,
> MemoryRegionSection *sec)
> >      XenPCIPassthroughState *s = container_of(l, XenPCIPassthroughState,
> >                                               memory_listener);
> >
> > -    memory_region_ref(sec->mr);
> >      xen_pt_region_update(s, sec, true);
> >  }
> >
> > @@ -598,7 +597,6 @@ static void xen_pt_region_del(MemoryListener *l,
> MemoryRegionSection *sec)
> >                                               memory_listener);
> >
> >      xen_pt_region_update(s, sec, false);
> > -    memory_region_unref(sec->mr);
> >  }
> >
> >  static void xen_pt_io_region_add(MemoryListener *l,
> MemoryRegionSection *sec)
> > @@ -606,7 +604,6 @@ static void xen_pt_io_region_add(MemoryListener
> *l, MemoryRegionSection *sec)
> >      XenPCIPassthroughState *s = container_of(l, XenPCIPassthroughState,
> >                                               io_listener);
> >
> > -    memory_region_ref(sec->mr);
> >      xen_pt_region_update(s, sec, true);
> >  }
> >
> > @@ -616,7 +613,6 @@ static void xen_pt_io_region_del(MemoryListener *l,
> MemoryRegionSection *sec)
> >                                               io_listener);
> >
> >      xen_pt_region_update(s, sec, false);
> > -    memory_region_unref(sec->mr);
> >  }
> >
> >  static const MemoryListener xen_pt_memory_listener = {
> > --
> > 1.9.1
> >
> 
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