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Re: [Qemu-devel] [PATCH v2 23/30] bus: do not unref hotplug handler
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH v2 23/30] bus: do not unref hotplug handler |
Date: |
Wed, 22 Feb 2017 12:33:25 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 |
On 21/02/2017 15:14, Marc-André Lureau wrote:
> Apparently, none of the bus owner give a reference to the hotplug
> handler property, do not unref it on bus release.
>
> Furthermore, a bus is allowed to be its own hotplug handler, which can
> be seen in qbus_set_bus_hotplug_handler() function. However, in this
> case, the reference can't be given to the property, or this will create
> a cyclic dependency and the bus will never be free.
>
> Each bus owner should manage the lifecycle of the hotplug handler.
>
> Signed-off-by: Marc-André Lureau <address@hidden>
Almost all qbus_set_hotplug_handler callers are using it to set the
parent device (that is, the "adapter" or "bridge", whatever you want to
call it) as the hotplug handler.
The exception is piix4_update_bus_hotplug. This one is the only case
where OBJ_PROP_LINK_UNREF_ON_RELEASE would be right. Luckily, there
_is_ a reference to that device somewhere else to keep it alive, namely
in /machine's acpi-device prop. So this case is a bit hacky (not your
fault) but works as well. In addition the PIIX4_PM device is not
hot(un)pluggable.
Can you please add a comment to piix4_update_bus_hotplug explaining that
the PIIX4PMState cannot outlive the PCIBus, because /machine keeps it alive?
>
> diff --git a/hw/core/bus.c b/hw/core/bus.c
> index cf383fc1af..4651f24486 100644
> --- a/hw/core/bus.c
> +++ b/hw/core/bus.c
> @@ -197,7 +197,7 @@ static void qbus_initfn(Object *obj)
> TYPE_HOTPLUG_HANDLER,
> (Object **)&bus->hotplug_handler,
> object_property_allow_set_link,
> - OBJ_PROP_LINK_UNREF_ON_RELEASE,
> + 0,
> NULL);
> object_property_add_bool(obj, "realized",
> bus_get_realized, bus_set_realized, NULL);
> --
> 2.11.0.295.gd7dffce1c.dirty
>
>
>
- Re: [Qemu-devel] [PATCH v2 16/30] tests: fix eepro100-test leak, (continued)
- [Qemu-devel] [PATCH v2 17/30] tests: fix tco-test leaks, Marc-André Lureau, 2017/02/21
- [Qemu-devel] [PATCH v2 18/30] tests: fix e1000-test leak, Marc-André Lureau, 2017/02/21
- [Qemu-devel] [PATCH v2 19/30] tests: fix i440fx-test leaks, Marc-André Lureau, 2017/02/21
- [Qemu-devel] [PATCH v2 20/30] tests: fix e1000e leaks, Marc-André Lureau, 2017/02/21
- [Qemu-devel] [PATCH v2 21/30] tests: fix virtio-scsi-test leak, Marc-André Lureau, 2017/02/21
- [Qemu-devel] [PATCH v2 22/30] tests: fix virtio-9p-test leaks, Marc-André Lureau, 2017/02/21
- [Qemu-devel] [PATCH v2 23/30] bus: do not unref hotplug handler, Marc-André Lureau, 2017/02/21
- Re: [Qemu-devel] [PATCH v2 23/30] bus: do not unref hotplug handler,
Paolo Bonzini <=
- [Qemu-devel] [PATCH v2 24/30] usb: replace handle_destroy with unrealize, Marc-André Lureau, 2017/02/21
- [Qemu-devel] [PATCH v2 26/30] tests: allows to run single test in usb-hcd-ehci-test, Marc-André Lureau, 2017/02/21
- [Qemu-devel] [PATCH v2 25/30] usb: release the created buses, Marc-André Lureau, 2017/02/21
- [Qemu-devel] [PATCH v2 27/30] tests: fix usb-test leaks, Marc-André Lureau, 2017/02/21