Patchwork weird qdev error

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Submitter Anthony Liguori
Date Feb. 12, 2012, 5:38 p.m.
Message ID <4F37F910.5030400@codemonkey.ws>
Download mbox | patch
Permalink /patch/140820/
State New
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Comments

Anthony Liguori - Feb. 12, 2012, 5:38 p.m.
On 02/12/2012 11:31 AM, Michael S. Tsirkin wrote:
> On Sun, Feb 12, 2012 at 07:07:43PM +0200, Michael S. Tsirkin wrote:
>> I got this assert when working on qemu: pci hotplug
>> callback failed so qdev_free was called.
>>
>> (gdb) where
>> #0  0x00007ffff5fa1905 in raise () from /lib64/libc.so.6
>> #1  0x00007ffff5fa30e5 in abort () from /lib64/libc.so.6
>> #2  0x00007ffff7413a7f in g_assertion_message () from
>> /lib64/libglib-2.0.so.0
>> #3  0x00007ffff7414020 in g_assertion_message_expr () from
>> /lib64/libglib-2.0.so.0
>> #4  0x00007ffff7e452a9 in object_delete (obj=0x7ffff9124e60) at
>> qom/object.c:375
>> #5  0x00007ffff7e2f5d4 in qdev_free (dev=0x7ffff9124e60)
>>      at /home/mst/scm/qemu/hw/qdev.c:250
>> #6  qdev_init (dev=0x7ffff9124e60) at /home/mst/scm/qemu/hw/qdev.c:149
>> #7  0x00007ffff7e2a7fe in qdev_device_add (opts=0x7ffff8b0d3a0)
>>      at /home/mst/scm/qemu/hw/qdev-monitor.c:473
>> #8  0x00007ffff7e06da9 in device_init_func (opts=<value optimized out>,
>>      opaque=<value optimized out>) at /home/mst/scm/qemu/vl.c:1754
>> #9  0x00007ffff7e3737a in qemu_opts_foreach (list=<value optimized out>,
>> func=
>>      0x7ffff7e06d90<device_init_func>, opaque=0x0,
>>      abort_on_failure=<value optimized out>) at qemu-option.c:1048
>> #10 0x00007ffff7e09cdb in main (argc=<value optimized out>, argv=<value
>> optimized out>,
>>      envp=<value optimized out>) at /home/mst/scm/qemu/vl.c:3407
>> (gdb) frame 6
>> #6  qdev_init (dev=0x7ffff9124e60) at /home/mst/scm/qemu/hw/qdev.c:149
>> 149             qdev_free(dev);
>>
>> The problems seems to be that
>> pci_qdev_init calls do_pci_unregister_device on
>> hotplug  error which will free the device twice?
>
> Here's a reproducer to a similar error in property parsing:
>
> qemu-system-x86_64  -enable-kvm -m 1G -drive file=/home/mst/rhel6.qcow2
> -netdev user,id=bar -net
> nic,netdev=bar,model=e1000,macaddr=52:54:00:12:34:57  -redir
> tcp:8022::22 -device virtio-net-pci,netdev=foo,mac=5854:00:12:34:56
> -netdev
> tap,id=foo,ifname=msttap0,script=/home/mst/ifup,downscript=no,vhost=on
> -vnc :1 -monitor stdio

Here's the fix.  I need to do some regression testing and then I'll post as a 
proper top-level patch.

Thanks for the report.

Regards,

Anthony Liguori

>
>
>
>> --
>> MST
Michael S. Tsirkin - Feb. 12, 2012, 5:57 p.m.
On Sun, Feb 12, 2012 at 11:38:24AM -0600, Anthony Liguori wrote:
> On 02/12/2012 11:31 AM, Michael S. Tsirkin wrote:
> >On Sun, Feb 12, 2012 at 07:07:43PM +0200, Michael S. Tsirkin wrote:
> >>I got this assert when working on qemu: pci hotplug
> >>callback failed so qdev_free was called.
> >>
> >>(gdb) where
> >>#0  0x00007ffff5fa1905 in raise () from /lib64/libc.so.6
> >>#1  0x00007ffff5fa30e5 in abort () from /lib64/libc.so.6
> >>#2  0x00007ffff7413a7f in g_assertion_message () from
> >>/lib64/libglib-2.0.so.0
> >>#3  0x00007ffff7414020 in g_assertion_message_expr () from
> >>/lib64/libglib-2.0.so.0
> >>#4  0x00007ffff7e452a9 in object_delete (obj=0x7ffff9124e60) at
> >>qom/object.c:375
> >>#5  0x00007ffff7e2f5d4 in qdev_free (dev=0x7ffff9124e60)
> >>     at /home/mst/scm/qemu/hw/qdev.c:250
> >>#6  qdev_init (dev=0x7ffff9124e60) at /home/mst/scm/qemu/hw/qdev.c:149
> >>#7  0x00007ffff7e2a7fe in qdev_device_add (opts=0x7ffff8b0d3a0)
> >>     at /home/mst/scm/qemu/hw/qdev-monitor.c:473
> >>#8  0x00007ffff7e06da9 in device_init_func (opts=<value optimized out>,
> >>     opaque=<value optimized out>) at /home/mst/scm/qemu/vl.c:1754
> >>#9  0x00007ffff7e3737a in qemu_opts_foreach (list=<value optimized out>,
> >>func=
> >>     0x7ffff7e06d90<device_init_func>, opaque=0x0,
> >>     abort_on_failure=<value optimized out>) at qemu-option.c:1048
> >>#10 0x00007ffff7e09cdb in main (argc=<value optimized out>, argv=<value
> >>optimized out>,
> >>     envp=<value optimized out>) at /home/mst/scm/qemu/vl.c:3407
> >>(gdb) frame 6
> >>#6  qdev_init (dev=0x7ffff9124e60) at /home/mst/scm/qemu/hw/qdev.c:149
> >>149             qdev_free(dev);
> >>
> >>The problems seems to be that
> >>pci_qdev_init calls do_pci_unregister_device on
> >>hotplug  error which will free the device twice?
> >
> >Here's a reproducer to a similar error in property parsing:
> >
> >qemu-system-x86_64  -enable-kvm -m 1G -drive file=/home/mst/rhel6.qcow2
> >-netdev user,id=bar -net
> >nic,netdev=bar,model=e1000,macaddr=52:54:00:12:34:57  -redir
> >tcp:8022::22 -device virtio-net-pci,netdev=foo,mac=5854:00:12:34:56
> >-netdev
> >tap,id=foo,ifname=msttap0,script=/home/mst/ifup,downscript=no,vhost=on
> >-vnc :1 -monitor stdio
> 
> Here's the fix.  I need to do some regression testing and then I'll
> post as a proper top-level patch.
> 
> Thanks for the report.
> 
> Regards,
> 
> Anthony Liguori
> 
> >
> >
> >
> >>--
> >>MST
> 

> >From b7fc6f1eb7c5e041eac7d610061a1be950707e5b Mon Sep 17 00:00:00 2001
> From: Anthony Liguori <aliguori@us.ibm.com>
> Date: Sun, 12 Feb 2012 11:36:24 -0600
> Subject: [PATCH] device_add: don't add a /peripheral link until init is complete
> 
> Otherwise we end up with a dangling reference which causes qdev_free() to fail.
> 
> Reported-by: Michael Tsirkin <mst@redhat.com>
> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

This handles the option parsing but what about hotplug
failures (when bus->hotplug returns an error)?

> ---
>  hw/qdev-monitor.c |   18 ++++++++++--------
>  1 files changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/hw/qdev-monitor.c b/hw/qdev-monitor.c
> index 49f13ca..a310cc7 100644
> --- a/hw/qdev-monitor.c
> +++ b/hw/qdev-monitor.c
> @@ -457,6 +457,16 @@ DeviceState *qdev_device_add(QemuOpts *opts)
>      id = qemu_opts_id(opts);
>      if (id) {
>          qdev->id = id;
> +    }
> +    if (qemu_opt_foreach(opts, set_property, qdev, 1) != 0) {
> +        qdev_free(qdev);
> +        return NULL;
> +    }
> +    if (qdev_init(qdev) < 0) {
> +        qerror_report(QERR_DEVICE_INIT_FAILED, driver);
> +        return NULL;
> +    }
> +    if (qdev->id) {
>          object_property_add_child(qdev_get_peripheral(), qdev->id,
>                                    OBJECT(qdev), NULL);
>      } else {
> @@ -466,14 +476,6 @@ DeviceState *qdev_device_add(QemuOpts *opts)
>                                    OBJECT(qdev), NULL);
>          g_free(name);
>      }        
> -    if (qemu_opt_foreach(opts, set_property, qdev, 1) != 0) {
> -        qdev_free(qdev);
> -        return NULL;
> -    }
> -    if (qdev_init(qdev) < 0) {
> -        qerror_report(QERR_DEVICE_INIT_FAILED, driver);
> -        return NULL;
> -    }
>      qdev->opts = opts;
>      return qdev;
>  }
> -- 
> 1.7.4.1
>
Anthony Liguori - Feb. 12, 2012, 8:04 p.m.
On 02/12/2012 11:57 AM, Michael S. Tsirkin wrote:
> On Sun, Feb 12, 2012 at 11:38:24AM -0600, Anthony Liguori wrote:
>> From: Anthony Liguori<aliguori@us.ibm.com>
>> Date: Sun, 12 Feb 2012 11:36:24 -0600
>> Subject: [PATCH] device_add: don't add a /peripheral link until init is complete
>>
>> Otherwise we end up with a dangling reference which causes qdev_free() to fail.
>>
>> Reported-by: Michael Tsirkin<mst@redhat.com>
>> Signed-off-by: Anthony Liguori<aliguori@us.ibm.com>
>
> This handles the option parsing but what about hotplug
> failures (when bus->hotplug returns an error)?

Sorry, I don't follow.

The assert you reported was that object_free() noted a reference count of !0 
which indicates something else was holding the reference to the object.  In this 
case, it was the child link in /peripheral.

By delaying creating the link in /peripheral, we eliminate the problem completely.

BTW, the explicit calls to do_pci_unregister are redundant.  finalize() will be 
called during cleanup which means exit() will be invoked (which already calls 
do_pci_unregister).  I'm not sure why this isn't failing more aggressively but 
it looks clearly wrong to me.

Regards,

Anthony Liguori
Michael S. Tsirkin - Feb. 12, 2012, 8:15 p.m.
On Sun, Feb 12, 2012 at 02:04:29PM -0600, Anthony Liguori wrote:
> On 02/12/2012 11:57 AM, Michael S. Tsirkin wrote:
> >On Sun, Feb 12, 2012 at 11:38:24AM -0600, Anthony Liguori wrote:
> >>From: Anthony Liguori<aliguori@us.ibm.com>
> >>Date: Sun, 12 Feb 2012 11:36:24 -0600
> >>Subject: [PATCH] device_add: don't add a /peripheral link until init is complete
> >>
> >>Otherwise we end up with a dangling reference which causes qdev_free() to fail.
> >>
> >>Reported-by: Michael Tsirkin<mst@redhat.com>
> >>Signed-off-by: Anthony Liguori<aliguori@us.ibm.com>
> >
> >This handles the option parsing but what about hotplug
> >failures (when bus->hotplug returns an error)?
> 
> Sorry, I don't follow.
> 
> The assert you reported was that object_free() noted a reference
> count of !0 which indicates something else was holding the reference
> to the object.  In this case, it was the child link in /peripheral.
> 
> By delaying creating the link in /peripheral, we eliminate the problem completely.

Th other problem was internal in pci which calls ->hostplug
during initialization. This doesn't seem affected?
But I didn't try, maybe I misundertand.

> BTW, the explicit calls to do_pci_unregister are redundant.
> finalize() will be called during cleanup which means exit() will be
> invoked (which already calls do_pci_unregister).  I'm not sure why
> this isn't failing more aggressively but it looks clearly wrong to
> me.
> 
> Regards,
> 
> Anthony Liguori

Me too. Want to try to drop them?
Anthony Liguori - Feb. 12, 2012, 8:19 p.m.
On 02/12/2012 02:15 PM, Michael S. Tsirkin wrote:
> On Sun, Feb 12, 2012 at 02:04:29PM -0600, Anthony Liguori wrote:
>> On 02/12/2012 11:57 AM, Michael S. Tsirkin wrote:
>>> On Sun, Feb 12, 2012 at 11:38:24AM -0600, Anthony Liguori wrote:
>>>> From: Anthony Liguori<aliguori@us.ibm.com>
>>>> Date: Sun, 12 Feb 2012 11:36:24 -0600
>>>> Subject: [PATCH] device_add: don't add a /peripheral link until init is complete
>>>>
>>>> Otherwise we end up with a dangling reference which causes qdev_free() to fail.
>>>>
>>>> Reported-by: Michael Tsirkin<mst@redhat.com>
>>>> Signed-off-by: Anthony Liguori<aliguori@us.ibm.com>
>>>
>>> This handles the option parsing but what about hotplug
>>> failures (when bus->hotplug returns an error)?
>>
>> Sorry, I don't follow.
>>
>> The assert you reported was that object_free() noted a reference
>> count of !0 which indicates something else was holding the reference
>> to the object.  In this case, it was the child link in /peripheral.
>>
>> By delaying creating the link in /peripheral, we eliminate the problem completely.
>
> Th other problem was internal in pci which calls ->hostplug
> during initialization. This doesn't seem affected?
> But I didn't try, maybe I misundertand.

Yeah, from qdev's perspective it's all just init failing.  hotplug is entirely a 
PCI concept.

>
>> BTW, the explicit calls to do_pci_unregister are redundant.
>> finalize() will be called during cleanup which means exit() will be
>> invoked (which already calls do_pci_unregister).  I'm not sure why
>> this isn't failing more aggressively but it looks clearly wrong to
>> me.
>>
>> Regards,
>>
>> Anthony Liguori
>
> Me too. Want to try to drop them?

Yeah, I'll make this a two patch series.

Regards,

Anthony Liguori

>
Michael S. Tsirkin - Feb. 13, 2012, 12:17 a.m.
On Sun, Feb 12, 2012 at 02:19:19PM -0600, Anthony Liguori wrote:
> On 02/12/2012 02:15 PM, Michael S. Tsirkin wrote:
> >On Sun, Feb 12, 2012 at 02:04:29PM -0600, Anthony Liguori wrote:
> >>On 02/12/2012 11:57 AM, Michael S. Tsirkin wrote:
> >>>On Sun, Feb 12, 2012 at 11:38:24AM -0600, Anthony Liguori wrote:
> >>>>From: Anthony Liguori<aliguori@us.ibm.com>
> >>>>Date: Sun, 12 Feb 2012 11:36:24 -0600
> >>>>Subject: [PATCH] device_add: don't add a /peripheral link until init is complete
> >>>>
> >>>>Otherwise we end up with a dangling reference which causes qdev_free() to fail.
> >>>>
> >>>>Reported-by: Michael Tsirkin<mst@redhat.com>
> >>>>Signed-off-by: Anthony Liguori<aliguori@us.ibm.com>
> >>>
> >>>This handles the option parsing but what about hotplug
> >>>failures (when bus->hotplug returns an error)?
> >>
> >>Sorry, I don't follow.
> >>
> >>The assert you reported was that object_free() noted a reference
> >>count of !0 which indicates something else was holding the reference
> >>to the object.  In this case, it was the child link in /peripheral.
> >>
> >>By delaying creating the link in /peripheral, we eliminate the problem completely.
> >
> >Th other problem was internal in pci which calls ->hostplug
> >during initialization. This doesn't seem affected?
> >But I didn't try, maybe I misundertand.
> 
> Yeah, from qdev's perspective it's all just init failing.  hotplug
> is entirely a PCI concept.
> 
> >
> >>BTW, the explicit calls to do_pci_unregister are redundant.
> >>finalize() will be called during cleanup which means exit() will be
> >>invoked (which already calls do_pci_unregister).  I'm not sure why
> >>this isn't failing more aggressively but it looks clearly wrong to
> >>me.
> >>
> >>Regards,
> >>
> >>Anthony Liguori
> >
> >Me too. Want to try to drop them?
> 
> Yeah, I'll make this a two patch series.
> 
> Regards,
> 
> Anthony Liguori


I also see this:

device_add virtio-net-pci,netdev=foo,mac=52:54:00:12:34:56,id=bla
device_del bla
*** glibc detected *** /home/mst/qemu-test/bin/qemu-system-x86_64:
corrupted double-linked list: 0x00007fae434565a0 ***

Am I alone?
Michael S. Tsirkin - Feb. 13, 2012, 1:18 a.m.
On Mon, Feb 13, 2012 at 02:17:35AM +0200, Michael S. Tsirkin wrote:
> On Sun, Feb 12, 2012 at 02:19:19PM -0600, Anthony Liguori wrote:
> > On 02/12/2012 02:15 PM, Michael S. Tsirkin wrote:
> > >On Sun, Feb 12, 2012 at 02:04:29PM -0600, Anthony Liguori wrote:
> > >>On 02/12/2012 11:57 AM, Michael S. Tsirkin wrote:
> > >>>On Sun, Feb 12, 2012 at 11:38:24AM -0600, Anthony Liguori wrote:
> > >>>>From: Anthony Liguori<aliguori@us.ibm.com>
> > >>>>Date: Sun, 12 Feb 2012 11:36:24 -0600
> > >>>>Subject: [PATCH] device_add: don't add a /peripheral link until init is complete
> > >>>>
> > >>>>Otherwise we end up with a dangling reference which causes qdev_free() to fail.
> > >>>>
> > >>>>Reported-by: Michael Tsirkin<mst@redhat.com>
> > >>>>Signed-off-by: Anthony Liguori<aliguori@us.ibm.com>
> > >>>
> > >>>This handles the option parsing but what about hotplug
> > >>>failures (when bus->hotplug returns an error)?
> > >>
> > >>Sorry, I don't follow.
> > >>
> > >>The assert you reported was that object_free() noted a reference
> > >>count of !0 which indicates something else was holding the reference
> > >>to the object.  In this case, it was the child link in /peripheral.
> > >>
> > >>By delaying creating the link in /peripheral, we eliminate the problem completely.
> > >
> > >Th other problem was internal in pci which calls ->hostplug
> > >during initialization. This doesn't seem affected?
> > >But I didn't try, maybe I misundertand.
> > 
> > Yeah, from qdev's perspective it's all just init failing.  hotplug
> > is entirely a PCI concept.
> > 
> > >
> > >>BTW, the explicit calls to do_pci_unregister are redundant.
> > >>finalize() will be called during cleanup which means exit() will be
> > >>invoked (which already calls do_pci_unregister).  I'm not sure why
> > >>this isn't failing more aggressively but it looks clearly wrong to
> > >>me.
> > >>
> > >>Regards,
> > >>
> > >>Anthony Liguori
> > >
> > >Me too. Want to try to drop them?
> > 
> > Yeah, I'll make this a two patch series.
> > 
> > Regards,
> > 
> > Anthony Liguori
> 
> 
> I also see this:
> 
> device_add virtio-net-pci,netdev=foo,mac=52:54:00:12:34:56,id=bla
> device_del bla
> *** glibc detected *** /home/mst/qemu-test/bin/qemu-system-x86_64:
> corrupted double-linked list: 0x00007fae434565a0 ***
> 
> Am I alone?
> 
> 


Tried some tracing:  I set breakpoint at g_free
and gave the device_del command.

(gdb) b g_free
Breakpoint 3 at 0x7ffff73f55b0
(gdb) c
Continuing.

Program received signal SIGTSTP, Stopped (user).
[Switching to Thread 0x7fffaf1a3700 (LWP 22749)]
0x00007ffff6ae074b in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
(gdb) c
Continuing.

Program received signal SIGTSTP, Stopped (user).
[Switching to Thread 0x7ffff4b28700 (LWP 22727)]
0x00007ffff6ae03cc in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
(gdb) continue
Continuing.

Program received signal SIGTSTP, Stopped (user).
[Switching to Thread 0x7ffff7cb3700 (LWP 22712)]
0x00007ffff604c383 in select () from /lib64/libc.so.6
(gdb) continue
Continuing.
[Thread 0x7fffaf1a3700 (LWP 22749) exited]


Breakpoint 3, 0x00007ffff73f55b0 in g_free () from /lib64/libglib-2.0.so.0
(gdb) continue
Continuing.
(qemu) device_del bla

Breakpoint 3, 0x00007ffff73f55b0 in g_free () from /lib64/libglib-2.0.so.0
(gdb) where
#0  0x00007ffff73f55b0 in g_free () from /lib64/libglib-2.0.so.0
#1  0x00007ffff7ec1d60 in monitor_parse_command (mon=0x7ffff8b207a0, 
    cmdline=<value optimized out>, qdict=0x7ffff9161660)
    at /home/mst/scm/qemu/monitor.c:3724
#2  0x00007ffff7ec2684 in handle_user_command (mon=0x7ffff8b207a0, cmdline=
    0x7ffff8c86a30 "device_del bla") at /home/mst/scm/qemu/monitor.c:3803
#3  0x00007ffff7ec2b6e in monitor_command_cb (mon=0x7ffff8b207a0, 
    cmdline=<value optimized out>, opaque=<value optimized out>)
    at /home/mst/scm/qemu/monitor.c:4436
#4  0x00007ffff7e463ed in readline_handle_byte (rs=0x7ffff8c86a30, 
    ch=<value optimized out>) at readline.c:370
#5  0x00007ffff7ec28b8 in monitor_read (opaque=<value optimized out>, buf=
    0x7fffffffce20 "\r\023\f\366\377\177", size=1) at /home/mst/scm/qemu/monitor.c:4422
#6  0x00007ffff7e313bb in qemu_chr_be_write (opaque=0x7ffff8b0ca00) at qemu-char.c:163
#7  fd_chr_read (opaque=0x7ffff8b0ca00) at qemu-char.c:587
#8  0x00007ffff7d7c967 in qemu_iohandler_poll (readfds=0x7fffffffdfb0, writefds=
    0x7fffffffdf30, xfds=<value optimized out>, ret=<value optimized out>)
    at iohandler.c:121
#9  0x00007ffff7e1085f in main_loop_wait (nonblocking=<value optimized out>)
    at main-loop.c:464
#10 0x00007ffff7e09284 in main_loop (argc=<value optimized out>, 
    argv=<value optimized out>, envp=<value optimized out>)
    at /home/mst/scm/qemu/vl.c:1482
#11 main (argc=<value optimized out>, argv=<value optimized out>, 
    envp=<value optimized out>) at /home/mst/scm/qemu/vl.c:3525
(gdb) frame 1
#1  0x00007ffff7ec1d60 in monitor_parse_command (mon=0x7ffff8b207a0, 
    cmdline=<value optimized out>, qdict=0x7ffff9161660)
    at /home/mst/scm/qemu/monitor.c:3724
3724            g_free(key);
(gdb) p key
$1 = 0x7ffff9166820 "id"
(gdb) continue
Continuing.

Breakpoint 3, 0x00007ffff73f55b0 in g_free () from /lib64/libglib-2.0.so.0
(gdb) where
#0  0x00007ffff73f55b0 in g_free () from /lib64/libglib-2.0.so.0
#1  0x00007ffff7e42fd4 in object_property_del (obj=0x7ffff8ca79d0, 
    name=<value optimized out>, errp=<value optimized out>) at qom/object.c:629
#2  0x00007ffff7e4308d in object_property_del_child (obj=0x7ffff9123e50)
    at qom/object.c:310
#3  object_unparent (obj=0x7ffff9123e50) at qom/object.c:318
#4  0x00007ffff7de0a0d in pci_unplug_device (qdev=<value optimized out>)
    at /home/mst/scm/qemu/hw/pci.c:1521
#5  0x00007ffff7ec26b5 in handle_user_command (mon=0x7ffff8b207a0, 
    cmdline=<value optimized out>) at /home/mst/scm/qemu/monitor.c:3813
#6  0x00007ffff7ec2b6e in monitor_command_cb (mon=0x7ffff8b207a0, 
    cmdline=<value optimized out>, opaque=<value optimized out>)
    at /home/mst/scm/qemu/monitor.c:4436
#7  0x00007ffff7e463ed in readline_handle_byte (rs=0x7ffff8c86a30, 
    ch=<value optimized out>) at readline.c:370
#8  0x00007ffff7ec28b8 in monitor_read (opaque=<value optimized out>, buf=
    0x7fffffffce20 "\r\023\f\366\377\177", size=1) at /home/mst/scm/qemu/monitor.c:4422
#9  0x00007ffff7e313bb in qemu_chr_be_write (opaque=0x7ffff8b0ca00) at qemu-char.c:163
#10 fd_chr_read (opaque=0x7ffff8b0ca00) at qemu-char.c:587
#11 0x00007ffff7d7c967 in qemu_iohandler_poll (readfds=0x7fffffffdfb0, writefds=
    0x7fffffffdf30, xfds=<value optimized out>, ret=<value optimized out>)
    at iohandler.c:121
#12 0x00007ffff7e1085f in main_loop_wait (nonblocking=<value optimized out>)
    at main-loop.c:464
#13 0x00007ffff7e09284 in main_loop (argc=<value optimized out>, 
    argv=<value optimized out>, envp=<value optimized out>)
    at /home/mst/scm/qemu/vl.c:1482
#14 main (argc=<value optimized out>, argv=<value optimized out>, 
---Type <return> to continue, or q <return> to quit---
    envp=<value optimized out>) at /home/mst/scm/qemu/vl.c:3525
(gdb) frame 1
#1  0x00007ffff7e42fd4 in object_property_del (obj=0x7ffff8ca79d0, 
    name=<value optimized out>, errp=<value optimized out>) at qom/object.c:629
629         g_free(prop->name);
(gdb) p prop->name
$2 = (gchar *) 0x7ffff9164510 "bla"
(gdb) continue
Continuing.

Breakpoint 3, 0x00007ffff73f55b0 in g_free () from /lib64/libglib-2.0.so.0
(gdb) frame 1
#1  0x00007ffff7e42fdd in object_property_del (obj=0x7ffff8ca79d0, 
    name=<value optimized out>, errp=<value optimized out>) at qom/object.c:630
630         g_free(prop->type);
(gdb) p prop->type
$3 = (gchar *) 0x7ffff9164580 "child<virtio-net-pci>"
(gdb) continue
Continuing.

Breakpoint 3, 0x00007ffff73f55b0 in g_free () from /lib64/libglib-2.0.so.0
(gdb) frame 1
#1  0x00007ffff7e4308d in object_property_del_child (obj=0x7ffff9123e50)
    at qom/object.c:310
310                 object_property_del(obj, prop->name, errp);
(gdb) p prop->name
$4 = (gchar *) 0x7ffff9164510 "\020h\026\371\377\177"

>>>>>>>>>>>>>>>>>>>>>>>>>>>>
It seems clear that there is at least a use after free
here.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>

This is not an immediate source of the crash, however.

Patch

From b7fc6f1eb7c5e041eac7d610061a1be950707e5b Mon Sep 17 00:00:00 2001
From: Anthony Liguori <aliguori@us.ibm.com>
Date: Sun, 12 Feb 2012 11:36:24 -0600
Subject: [PATCH] device_add: don't add a /peripheral link until init is complete

Otherwise we end up with a dangling reference which causes qdev_free() to fail.

Reported-by: Michael Tsirkin <mst@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
---
 hw/qdev-monitor.c |   18 ++++++++++--------
 1 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/hw/qdev-monitor.c b/hw/qdev-monitor.c
index 49f13ca..a310cc7 100644
--- a/hw/qdev-monitor.c
+++ b/hw/qdev-monitor.c
@@ -457,6 +457,16 @@  DeviceState *qdev_device_add(QemuOpts *opts)
     id = qemu_opts_id(opts);
     if (id) {
         qdev->id = id;
+    }
+    if (qemu_opt_foreach(opts, set_property, qdev, 1) != 0) {
+        qdev_free(qdev);
+        return NULL;
+    }
+    if (qdev_init(qdev) < 0) {
+        qerror_report(QERR_DEVICE_INIT_FAILED, driver);
+        return NULL;
+    }
+    if (qdev->id) {
         object_property_add_child(qdev_get_peripheral(), qdev->id,
                                   OBJECT(qdev), NULL);
     } else {
@@ -466,14 +476,6 @@  DeviceState *qdev_device_add(QemuOpts *opts)
                                   OBJECT(qdev), NULL);
         g_free(name);
     }        
-    if (qemu_opt_foreach(opts, set_property, qdev, 1) != 0) {
-        qdev_free(qdev);
-        return NULL;
-    }
-    if (qdev_init(qdev) < 0) {
-        qerror_report(QERR_DEVICE_INIT_FAILED, driver);
-        return NULL;
-    }
     qdev->opts = opts;
     return qdev;
 }
-- 
1.7.4.1