[Qemu-devel] bus_unparent() can go into infinite loop

[Markus Armbruster]

Reproducer (don't ask):

    $ qemu-system-arm -M virt -S -display none -drive 
if=scsi,id=foo,bus=1,file=tmp.qcow2 -device nec-usb-xhci -device 
usb-storage,drive=foo -device virtio-scsi-pci
    qemu-system-arm: -drive if=scsi,id=foo,bus=1,file=tmp.qcow2: Property 
'scsi-disk.drive' can't take value 'foo', it's in use
    qemu-system-arm: -drive if=scsi,id=foo,bus=1,file=tmp.qcow2: Setting drive 
property failed
    qemu-system-arm: -device virtio-scsi-pci: Setting drive property failed

Nevermind the silly error reporting, I got patches to clean that up.

Stuck in bus_unparent()'s loop:

    while ((kid = QTAILQ_FIRST(&bus->children)) != NULL) {
        DeviceState *dev = kid->child;
        object_unparent(OBJECT(dev));
    }

(gdb) bt
#0  bus_unparent (obj=<optimized out>)
    at /home/armbru/work/qemu/hw/core/qdev.c:727
#1  0x000055555583a165 in object_finalize_child_property (obj=<optimized out>, 
    name=<optimized out>, opaque=0x555556450060)
    at /home/armbru/work/qemu/qom/object.c:1079
#2  0x000055555583a40c in object_property_del (obj=0x55555644ff50, 
    name=0x555556696450 "scsi.1", errp=<optimized out>)
    at /home/armbru/work/qemu/qom/object.c:800
#3  0x000055555577f759 in device_unparent (obj=0x55555644ff50)
    at /home/armbru/work/qemu/hw/core/qdev.c:1230
#4  0x000055555583a165 in object_finalize_child_property (obj=<optimized out>, 
    name=<optimized out>, opaque=0x55555644ff50)
    at /home/armbru/work/qemu/qom/object.c:1079
#5  0x000055555583a40c in object_property_del (obj=0x55555644f540, 
    name=0x5555566b9620 "virtio-backend", errp=<optimized out>)
    at /home/armbru/work/qemu/qom/object.c:800
#6  0x00005555557800c6 in qdev_init (address@hidden)
    at /home/armbru/work/qemu/hw/core/qdev.c:186
#7  0x000055555582440e in virtio_scsi_pci_init_pci (vpci_dev=0x55555644f540)
    at /home/armbru/work/qemu/hw/virtio/virtio-pci.c:1157
#8  0x0000555555825fc8 in virtio_pci_init (pci_dev=<optimized out>)
    at /home/armbru/work/qemu/hw/virtio/virtio-pci.c:1018
#9  0x00005555557d6df7 in pci_qdev_init (qdev=0x55555644f540)
    at /home/armbru/work/qemu/hw/pci/pci.c:1775
#10 0x000055555577fbc4 in device_realize (dev=0x55555644f540, 
    errp=0x7fffffffda60) at /home/armbru/work/qemu/hw/core/qdev.c:247
#11 0x000055555578125d in device_set_realized (obj=0x55555644f540, 
    value=<optimized out>, errp=0x7fffffffdb98)
    at /home/armbru/work/qemu/hw/core/qdev.c:1040
#12 0x000055555583927e in property_set_bool (obj=0x55555644f540, 
    v=<optimized out>, opaque=0x555556698850, name=<optimized out>, 
    errp=0x7fffffffdb98) at /home/armbru/work/qemu/qom/object.c:1514
#13 0x000055555583bc67 in object_property_set_qobject (obj=0x55555644f540, 
    value=<optimized out>, name=0x5555559482fd "realized", errp=0x7fffffffdb98)
    at /home/armbru/work/qemu/qom/qom-qobject.c:24
#14 0x000055555583a7b0 in object_property_set_bool (
    address@hidden, address@hidden, 
    address@hidden "realized", address@hidden)
    at /home/armbru/work/qemu/qom/object.c:905
#15 0x000055555570d774 in qdev_device_add (opts=0x5555562a38c0)
    at /home/armbru/work/qemu/qdev-monitor.c:574
#16 0x0000555555716c79 in device_init_func (opts=<optimized out>, 
    opaque=<optimized out>) at /home/armbru/work/qemu/vl.c:2127
#17 0x00005555558f48eb in qemu_opts_foreach (list=<optimized out>, func=
    0x555555716c70 <device_init_func>, opaque=0x0, 
    abort_on_failure=<optimized out>)
    at /home/armbru/work/qemu/util/qemu-option.c:1057
#18 0x000055555560e39d in main (argc=<optimized out>, argv=<optimized out>, 
    envp=<optimized out>) at /home/armbru/work/qemu/vl.c:4244
(gdb) p dev->parent_obj.class->type->name
$5 = 0x55555626c3b0 "scsi-disk"
(gdb) p bus->name
$8 = 0x555556696430 "scsi.1"