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Re: [Qemu-devel] [PATCH v2 2/3] qdev: add cleanup logic in device_set_re
From: |
Gonglei (Arei) |
Subject: |
Re: [Qemu-devel] [PATCH v2 2/3] qdev: add cleanup logic in device_set_realized() to avoid resource leak |
Date: |
Tue, 26 Aug 2014 05:01:17 +0000 |
Hi, Peter.
Firstly, I appreciate your so careful and useful comments very much.
> -----Original Message-----
> From: address@hidden
> [mailto:address@hidden On Behalf Of Peter Crosthwaite
> Sent: Tuesday, August 26, 2014 10:25 AM
> To: Gonglei (Arei)
> Cc: address@hidden Developers; Huangweidong (C); Michael S. Tsirkin;
> Luonengjun; Huangpeng (Peter); Igor Mammedov; Paolo Bonzini; Andreas
> Färber
> Subject: Re: [Qemu-devel] [PATCH v2 2/3] qdev: add cleanup logic in
> device_set_realized() to avoid resource leak
>
> On Thu, Aug 21, 2014 at 12:11 PM, <address@hidden> wrote:
> > From: Gonglei <address@hidden>
> >
> > At present, this function doesn't have partial cleanup implemented,
> > which will cause resource leak in some scenarios.
> >
> > Example:
> >
> > 1. Assuming that "dc->realize(dev, &local_err)" execute successful
> > and local_err == NULL;
> > 2. Executing device hotplug in hotplug_handler_plug(), but failed
> > (It is prone to occur). Then local_err != NULL;
> > 3. error_propagate(errp, local_err) and return. But the resources
> > which been allocated in dc->realize() will be leaked.
> > Simple backtrace:
> > dc->realize()
> > |->device_realize
> > |->pci_qdev_init()
> > |->do_pci_register_device()
> > |->etc.
> >
> > Adding fuller cleanup logic which assure that function can
> > goto appropriate error label as local_err population is
> > detected as each relevant point.
> >
> > Signed-off-by: Gonglei <address@hidden>
> > ---
> > hw/core/qdev.c | 58
> ++++++++++++++++++++++++++++++++++++++--------------------
> > 1 file changed, 38 insertions(+), 20 deletions(-)
> >
> > diff --git a/hw/core/qdev.c b/hw/core/qdev.c
> > index 4a1ac5b..c1a36f0 100644
> > --- a/hw/core/qdev.c
> > +++ b/hw/core/qdev.c
> > @@ -834,12 +834,14 @@ static void device_set_realized(Object *obj, bool
> value, Error **errp)
> > dc->realize(dev, &local_err);
> > }
> >
> > - if (dev->parent_bus && dev->parent_bus->hotplug_handler &&
> > - local_err == NULL) {
> > + if (local_err != NULL) {
> > + goto fail;
> > + }
> > +
> > + if (dev->parent_bus && dev->parent_bus->hotplug_handler) {
> > hotplug_handler_plug(dev->parent_bus->hotplug_handler,
> > dev, &local_err);
> > - } else if (local_err == NULL &&
> > - object_dynamic_cast(qdev_get_machine(),
> TYPE_MACHINE)) {
> > + } else if (object_dynamic_cast(qdev_get_machine(),
> TYPE_MACHINE)) {
> > HotplugHandler *hotplug_ctrl;
> > MachineState *machine = MACHINE(qdev_get_machine());
> > MachineClass *mc = MACHINE_GET_CLASS(machine);
> > @@ -852,21 +854,25 @@ static void device_set_realized(Object *obj, bool
> value, Error **errp)
> > }
> > }
> >
> > - if (qdev_get_vmsd(dev) && local_err == NULL) {
> > + if (local_err != NULL) {
> > + goto post_realize_fail;
> > + }
> > +
> > + if (qdev_get_vmsd(dev)) {
> > vmstate_register_with_alias_id(dev, -1,
> qdev_get_vmsd(dev), dev,
> >
> dev->instance_id_alias,
> >
> dev->alias_required_for_version);
> > }
> > - if (local_err == NULL) {
> > - QLIST_FOREACH(bus, &dev->child_bus, sibling) {
> > - object_property_set_bool(OBJECT(bus), true, "realized",
> > - &local_err);
> > - if (local_err != NULL) {
> > - break;
> > - }
> > +
> > + QLIST_FOREACH(bus, &dev->child_bus, sibling) {
> > + object_property_set_bool(OBJECT(bus), true, "realized",
> > + &local_err);
> > + if (local_err != NULL) {
> > + goto set_bool_fail;
>
> This is actually quite tricky to cleanup right, as if this borks part
> way through the iterations wont you need to recursive unrealize any
> children that have already been successfully realized?
>
Yes. I think we should unrealize those children.
> > }
> > }
> > - if (dev->hotplugged && local_err == NULL) {
> > +
> > + if (dev->hotplugged) {
> > device_reset(dev);
> > }
> > dev->pending_deleted_event = false;
> > @@ -875,24 +881,36 @@ static void device_set_realized(Object *obj, bool
> value, Error **errp)
> > object_property_set_bool(OBJECT(bus), false, "realized",
> > &local_err);
> > if (local_err != NULL) {
> > - break;
> > + goto fail;
> > }
>
> I'm starting the question the need for this break (or goto). If any
> one of the child unrealizations fails, then the iteration stops,
> inhibiting garbage collection (i..e one bad child, stops the cleanup
> for whole set). Should subsequent iterations of the loop continue (but
> you will need to set errp = NULL)?
>
IMHO, continue to cleanup for other children maybe a good idea.
> About my comment above, you may be able to inspect the child realized
> property, to recycle this loop as the cleanup needed for partial child
> realization fail. That is, always loop through the whole list and if
> the child is is realized, unrealize it.
>
Yes.
> > }
> > - if (qdev_get_vmsd(dev) && local_err == NULL) {
> > + if (qdev_get_vmsd(dev)) {
> > vmstate_unregister(dev, qdev_get_vmsd(dev), dev);
> > }
>
> From here on seems very similar to the fail conditions now. Is there
> code share opportunity? - to just jump to what you have labelled as
> set_bool_fail and let the error handler implement the unrealization
> process?
If we share those code, whether it will people feel puzzled?
When the normal unrealized operation changed into error handler
implementation.
Best regards,
-Gonglei
> If the realize success path returns from inside the if, then
> you don't need a success path goto in unrealize path either. Here's
> the basic idea:
>
> if (doing_realize) {
> foo(&err);
> if (err) goto foo_fail;
> bar(&err);
> if (err) goto bar_fail;
> baz(&err);
> if (err) goto baz_fail;
> dc->realized = true;
> return;
> } /* else - doing an unrealize */
> un_baz();
> baz_fail:
> un_bar();
> bar_fail:
> un_foo();
> foo_fail:
> dc->realized = false;
> return;
>
> > - if (dc->unrealize && local_err == NULL) {
> > + if (dc->unrealize) {
> > dc->unrealize(dev, &local_err);
> > }
> > dev->pending_deleted_event = true;
> > - }
> >
> > - if (local_err != NULL) {
> > - error_propagate(errp, local_err);
> > - return;
> > + if (local_err != NULL) {
> > + goto fail;
> > + }
> > }
> >
> > dev->realized = value;
> > + return;
> > +
> > +set_bool_fail:
> > + if (qdev_get_vmsd(dev)) {
> > + vmstate_unregister(dev, qdev_get_vmsd(dev), dev);
> > + }
> > +post_realize_fail:
> > + if (dc->unrealize) {
> > + dc->unrealize(dev, NULL);
> > + }
> > +fail:
> > + error_propagate(errp, local_err);
>
> You would then conditionalise error propagation like in original code.
>
> Regards,
> Peter
>
> > + return;
> > }
> >
> > static bool device_get_hotpluggable(Object *obj, Error **errp)
> > --
> > 1.7.12.4
> >
> >
> >