On Mon, Nov 16, 2015 at 05:44:35PM +0100, Andreas Färber wrote:
> Am 16.11.2015 um 10:38 schrieb Andreas Färber:
> > Am 16.11.2015 um 09:16 schrieb Christian Borntraeger:
> >> On 11/16/2015 08:13 AM, Pavel Fedin wrote:
> >>>>>> (process:4102): GLib-CRITICAL **: g_hash_table_iter_next: assertion
> >>>>>> 'ri->version == ri->hash_table->version' failed
> >>>>>>
> >>>>>> (process:4102): GLib-CRITICAL **: g_hash_table_iter_next: assertion
> >>>>>> 'ri->version == ri->hash_table->version' failed
> >>>>>>
> >>>>>> (process:4102): GLib-CRITICAL **: iter_remove_or_steal: assertion
> >>>>>> 'ri->version == ri->hash_table->version' failed
> >>>
> >>> Wow... Actually this may come from attempts to modify the tree inside
> >>> iteration.
> >>>
> >>>> Thanks! sclp_init() seems to violate several QOM design principles in
> >>>> that it uses object_new() during TypeInfo::instance_init() and uses a
> >>>> TYPE_... constant as property name. But nothing else stands out
> >>>> immediately.
> >>>
> >>> I think we should refactor this and retry. If not all problems go away,
> >>> then we are indeed modifying the tree during iteration, and
> >>> we have to find some solution.
> >>
> >> David, Conny,
> >>
> >> the current tree of afaerber
> >>
> >> https://github.com/afaerber/qemu-cpu/commits/qom-next
> >>
> >> has this patch:
> >>
> >>> From: Pavel Fedin <p.fe...@samsung.com>
> >>>
> >>> ARM GICv3 systems with large number of CPUs create lots of IRQ pins. Since
> >>> every pin is represented as a property, number of these properties becomes
> >>> very large. Every property add first makes sure there's no duplicates.
> >>> Traversing the list becomes very slow, therefore qemu initialization takes
> >>> significant time (several seconds for e. g. 16 CPUs).
> >>>
> >>> This patch replaces list with GHashTable, making lookup very fast. The
> >>> only
> >>> drawback is that object_child_foreach() and
> >>> object_child_foreach_recursive()
> >>> cannot modify their objects during traversal, since GHashTableIter does
> >>> not
> >>> have modify-safe version. However, the code seems not to modify objects
> >>> via
> >>> these functions.
> >>>
> >>> Signed-off-by: Daniel P. Berrange <berra...@redhat.com>
> >>> Signed-off-by: Pavel Fedin <p.fe...@samsung.com>
> >>
> >> which causes failures in make check. A simple reproducer is
> >>
> >> qemu-system-s390x -device sclp,help
> >>
> >>
> >> any idea what would be the most simple fix?
> >> Can we refactor this to create the event facility and the bus in the
> >> machine or whatever?
> >
> > I believe it is rather a very general problem with the new
> > object_property_del_all() implementation. It iterates through
> > properties, releasing child<> and link<> properties, which results in an
> > unref, which at some point unparents that device, removing it in the
> > parent's properties hashtable while the parent is iterating through it.
> >
> > In this case it seems to be about the bus child<> on the event facility.
> >
> >>> I wonder... Could we have both list and hashtable? hashtable for
> >>> searching by name and list for iteration. In this case we would
> >>> not have to use glib's iterators, and would be free of problems with
> >>> them. Just keep the list and hashtable in sync.
> >>> Or, is there any hashtable implementation out there which would keep
> >>> iterators valid during modification?
> >>> OTOH, glib has a function "remove the element at iterator's position",
> >>> and we could postpone addition. So, perhaps, using both
> >>> containers would be an overkill, just refactor the code to adapt to the
> >>> new behavior.
> >
> > My idea, which I wanted to investigate after the weekend, is iterating
> > through the hashtable to create a list of prop->release functions and
> > call them only after finishing the iteration. That might not work
> > either, so we may need to loop over the releasing to allow for released
> > properties to disappear after prop->release().
>
> I went with the latter and squashed the attached fixup (without last two
> hunks, preparing a separate patch for that), interrupting each iteration
> after prop->release() to be safe. That seems to fix it.
>
> Will prepend and test Dan's unit test next.
> diff --git a/qom/object.c b/qom/object.c
> index 0ac3bc1..284fa38 100644
> --- a/qom/object.c
> +++ b/qom/object.c
> @@ -377,14 +377,22 @@ static void object_property_del_all(Object *obj)
> ObjectProperty *prop;
> GHashTableIter iter;
> gpointer key, value;
> + bool released;
>
> - g_hash_table_iter_init(&iter, obj->properties);
> - while (g_hash_table_iter_next(&iter, &key, &value)) {
> - prop = value;
> - if (prop->release) {
> - prop->release(obj, prop->name, prop->opaque);
> + do {
> + released = false;
> + g_hash_table_iter_init(&iter, obj->properties);
> + while (g_hash_table_iter_next(&iter, &key, &value)) {
> + prop = value;
> + if (prop->release) {
> + prop->release(obj, prop->name, prop->opaque);
> + prop->release = NULL;
> + released = true;
> + break;
> + }
> + g_hash_table_iter_remove(&iter);
> }
> - }
> + } while (released);
>
> g_hash_table_unref(obj->properties);
> }
> @@ -401,7 +409,15 @@ static void object_property_del_child(Object *obj,
> Object *child, Error **errp)
> if (object_property_is_child(prop) && prop->opaque == child) {
> if (prop->release) {
> prop->release(obj, prop->name, prop->opaque);
> + prop->release = NULL;
> }
> + break;
> + }
> + }
> + g_hash_table_iter_init(&iter, obj->properties);
> + while (g_hash_table_iter_next(&iter, &key, &value)) {
> + prop = value;
> + if (object_property_is_child(prop) && prop->opaque == child) {
> g_hash_table_iter_remove(&iter);
> break;
> }
> @@ -856,7 +872,7 @@ void object_ref(Object *obj)
> if (!obj) {
> return;
> }
> - atomic_inc(&obj->ref);
> + atomic_inc(&obj->ref);
> }
>
> void object_unref(Object *obj)
> @@ -864,7 +880,7 @@ void object_unref(Object *obj)
> if (!obj) {
> return;
> }
> - g_assert(obj->ref > 0);
> + g_assert_cmpint(obj->ref, >, 0);
>
> /* parent always holds a reference to its children */
> if (atomic_fetch_dec(&obj->ref) == 1) {
This looks good to me so can add Signed-off-by: Daniel P. Berrange
to this change.
Regards,
Daniel
--
|: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org -o- http://virt-manager.org :|
|: http://autobuild.org -o- http://search.cpan.org/~danberr/ :|
|: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|
