Re: [Qemu-devel] [PATCH] virtio-serial: Fix segfault on guest boot

[Amit Shah]

On (Thu) 16 Jun 2011 [13:38:49], Luiz Capitulino wrote:
> If I start qemu with:
> 
>  # qemu -hda disks/test.img -enable-kvm -m 1G -snapshot \
>         -device virtio-serial \
>         -chardev socket,host=localhost,port=1234,server,nowait,id=foo \
>         -device virtserialport,chardev=foo,name=org.qemu.guest_agent
> 
> I get a segfault when booting a Fedora 14 guest. The backtrace says:
>
>   Program terminated with signal 11, Segmentation fault.
>   #0  0x0000000000420850 in handle_control_message (vser=0x3732bd0, 
> buf=0x2c173e0, len=8) at 
> /home/lcapitulino/src/qmp-unstable/hw/virtio-serial-bus.c:335
>   335     info = DO_UPCAST(VirtIOSerialPortInfo, qdev, port->dev.info);

Strange, I've not seen it so far in my testing (neither in the daily
test runs of the virtio-serial testsuite).

> I've also bisected this and git points out to commit:
> 
>   commit a15bb0d6a981de749452a5180fc8084d625671da
>   Author: Markus Armbruster <address@hidden>
>   Date:   Wed May 25 14:21:13 2011 +0200
> 
>       virtio-serial: Drop redundant VirtIOSerialPort member info
> 
> I think what's happening is that the device is not initialized on a
> VIRTIO_CONSOLE_DEVICE_READY event. Moving the DO_UPCAST() call to
> the other events fixes the problem to me.
> 
> Signed-off-by: Luiz Capitulino <address@hidden>
> ---
>  hw/virtio-serial-bus.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/virtio-serial-bus.c b/hw/virtio-serial-bus.c
> index 9a12104..579f676 100644
> --- a/hw/virtio-serial-bus.c
> +++ b/hw/virtio-serial-bus.c
> @@ -332,8 +332,6 @@ static void handle_control_message(VirtIOSerial *vser, 
> void *buf, size_t len)
>      if (!port && cpkt.event != VIRTIO_CONSOLE_DEVICE_READY)
>          return;
>  
> -    info = DO_UPCAST(VirtIOSerialPortInfo, qdev, port->dev.info);
> -

Ah - this missed the !port check.  It should be possible to do this in
a 'if (port)' block instead of replicating in the individual case
statements.

Thanks for the debugging and patch; please update with the above and
I'll apply it to the virtio-serial tree.

                Amit