Re: [Qemu-devel] [PATCH] hmp: fix regression of HMP device_del auto-completion

[Marcel Apfelbaum]

On Thu, 2014-11-27 at 13:38 +0100, Igor Mammedov wrote:
> On Thu, 27 Nov 2014 13:41:07 +0200
> Marcel Apfelbaum <address@hidden> wrote:
> 
> > On Thu, 2014-11-27 at 19:35 +0800, Zhu Guihua wrote:
> > > On Thu, 2014-11-27 at 13:11 +0200, Marcel Apfelbaum wrote:
> > > > On Wed, 2014-11-26 at 13:05 -0500, Luiz Capitulino wrote:
> > > > > On Wed, 26 Nov 2014 13:50:01 +0200
> > > > > Marcel Apfelbaum <address@hidden> wrote:
> > > > > 
> > > > > > The commits:
> > > > > >  - 6a1fa9f5 (monitor: add del completion for peripheral device)
> > > > > >  - 66e56b13 (qdev: add qdev_build_hotpluggable_device_list helper)
> > > > > > 
> > > > > > cause a QEMU crash when trying to use HMP device_del 
> > > > > > auto-completion.
> > > > > > It can be easily reproduced by:
> > > > > >     <qemu-bin> -enable-kvm  ~/images/fedora.qcow2 -monitor stdio 
> > > > > > -device virtio-net-pci,id=vnet
> > > > > > 
> > > > > >     (qemu) device_del
> > > > > >     
> > > > > > /home/mapfelba/git/upstream/qemu/hw/core/qdev.c:941:qdev_build_hotpluggable_device_list:
> > > > > >  Object 0x7f6ce04e4fe0 is not an instance of type device
> > > > > >     Aborted (core dumped)
> > > > > > 
> > > > > > The root cause is qdev_build_hotpluggable_device_list going 
> > > > > > recursively over
> > > > > > all peripherals and their children assuming all are devices. It 
> > > > > > doesn't work
> > > > > > since PCI devices have at least on child which is a memory region 
> > > > > > (bus master).
> > > > > > 
> > > > > > Solved by observing that all devices appear as direct children of
> > > > > > /machine/peripheral container. No need of going recursively
> > > > > > over all the children.
> > > > > > 
> > > > > > Signed-off-by: Marcel Apfelbaum <address@hidden>
> > > > > 
> > > > > Peter, can you apply this patch directly to master to avoid me a pull
> > > > > request? Maybe it's a good idea to wait until tomorrow for more
> > > > > reviewers though.
> > > > Speaking of reviewers, I double checked the patch and indeed it solves
> > > > the crash, but the original patch has another semantic error.
> > > > It looks for hot-pluggable device and not *hot-plugged* ones.
> > > > 
> > > > I'll try to come with a solution fast. It should be a "hot-plugged" 
> > > > property somewhere...
> > > > 
> > > Hi Marcel,
> > > 
> > > May you give an example for a hot-plugged but non-hot-pluggable device?
> > I was talking about something different:
> > A hot-pluggable device that was not hot-plugged is assumed to be 
> > hot-unpluggable.
> That's applicable to most of devices.
> 
> > This is not true for pci-2-pci device.
> Do you have a reproducer?
Sure:
<qemu-bin> <img>  -device pci-bridge,chassis_nr=1,id=bridge

On monitor:
device_del bridge

And nothing happens since pci-2-pci can't be hot unplugged
The suspected reason is because it appears in ACPI tables. 

Thanks,
Marcel


> 
> > 
> > But this is another issue and can wait for 2.3.
> > So you patch was *almost* correct for looking hotpluggable devices,
> > the only problem we have is with pci-2-pci bridge (, and maybe with others 
> > that I don't know).
> > 
> > But for now, we should get the crash fix in and handle that separately
> > for 2.3. If anybody has a better idea, pleas advice.
> > 
> > Thanks,
> > Marcel
> > 
> > 
> >  
> > 
> > > 
> > > Regards,
> > > Zhu
> > > 
> > > > Thanks,
> > > > Marcel
> > > > 
> > > > 
> > > > > 
> > > > > Marcel, thanks a lot for taking care of this!
> > > > > 
> > > > > > ---
> > > > > >  hw/core/qdev.c         | 12 ++++++++++--
> > > > > >  include/hw/qdev-core.h |  2 +-
> > > > > >  monitor.c              | 11 ++++-------
> > > > > >  3 files changed, 15 insertions(+), 10 deletions(-)
> > > > > > 
> > > > > > diff --git a/hw/core/qdev.c b/hw/core/qdev.c
> > > > > > index 413b413..35fd00d 100644
> > > > > > --- a/hw/core/qdev.c
> > > > > > +++ b/hw/core/qdev.c
> > > > > > @@ -935,7 +935,7 @@ void qdev_alias_all_properties(DeviceState 
> > > > > > *target, Object *source)
> > > > > >      } while (class != object_class_by_name(TYPE_DEVICE));
> > > > > >  }
> > > > > >  
> > > > > > -int qdev_build_hotpluggable_device_list(Object *obj, void *opaque)
> > > > > > +static int qdev_add_hotpluggable_device(Object *obj, void *opaque)
> > > > > >  {
> > > > > >      GSList **list = opaque;
> > > > > >      DeviceState *dev = DEVICE(obj);
> > > > > > @@ -944,10 +944,18 @@ int 
> > > > > > qdev_build_hotpluggable_device_list(Object *obj, void *opaque)
> > > > > >          *list = g_slist_append(*list, dev);
> > > > > >      }
> > > > > >  
> > > > > > -    object_child_foreach(obj, qdev_build_hotpluggable_device_list, 
> > > > > > opaque);
> > > > > >      return 0;
> > > > > >  }
> > > > > >  
> > > > > > +GSList *qdev_build_hotpluggable_device_list(Object *peripheral)
> > > > > > +{
> > > > > > +    GSList *list = NULL;
> > > > > > +
> > > > > > +    object_child_foreach(peripheral, qdev_add_hotpluggable_device, 
> > > > > > &list);
> > > > > > +
> > > > > > +    return list;
> > > > > > +}
> > > > > > +
> > > > > >  static bool device_get_realized(Object *obj, Error **errp)
> > > > > >  {
> > > > > >      DeviceState *dev = DEVICE(obj);
> > > > > > diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
> > > > > > index d3a2940..589bbe7 100644
> > > > > > --- a/include/hw/qdev-core.h
> > > > > > +++ b/include/hw/qdev-core.h
> > > > > > @@ -365,7 +365,7 @@ extern int qdev_hotplug;
> > > > > >  
> > > > > >  char *qdev_get_dev_path(DeviceState *dev);
> > > > > >  
> > > > > > -int qdev_build_hotpluggable_device_list(Object *obj, void *opaque);
> > > > > > +GSList *qdev_build_hotpluggable_device_list(Object *peripheral);
> > > > > >  
> > > > > >  void qbus_set_hotplug_handler(BusState *bus, DeviceState *handler,
> > > > > >                                Error **errp);
> > > > > > diff --git a/monitor.c b/monitor.c
> > > > > > index fa00594..f1031a1 100644
> > > > > > --- a/monitor.c
> > > > > > +++ b/monitor.c
> > > > > > @@ -4321,17 +4321,14 @@ void object_add_completion(ReadLineState 
> > > > > > *rs, int nb_args, const char *str)
> > > > > >  static void peripheral_device_del_completion(ReadLineState *rs,
> > > > > >                                               const char *str, 
> > > > > > size_t len)
> > > > > >  {
> > > > > > -    Object *peripheral;
> > > > > > -    GSList *list = NULL, *item;
> > > > > > +    Object *peripheral = container_get(qdev_get_machine(), 
> > > > > > "/peripheral");
> > > > > > +    GSList *list, *item;
> > > > > >  
> > > > > > -    peripheral = object_resolve_path("/machine/peripheral/", NULL);
> > > > > > -    if (peripheral == NULL) {
> > > > > > +    list = qdev_build_hotpluggable_device_list(peripheral);
> > > > > > +    if (!list) {
> > > > > >          return;
> > > > > >      }
> > > > > >  
> > > > > > -    object_child_foreach(peripheral, 
> > > > > > qdev_build_hotpluggable_device_list,
> > > > > > -                         &list);
> > > > > > -
> > > > > >      for (item = list; item; item = g_slist_next(item)) {
> > > > > >          DeviceState *dev = item->data;
> > > > > >  
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