BUG: 'list_empty(&vgdev->free_vbufs)' is true!

[Jiri Slaby]

On 11/09/2016, 09:01 AM, Gerd Hoffmann wrote:
> On Di, 2016-11-08 at 22:37 +0200, Michael S. Tsirkin wrote:
>> On Mon, Nov 07, 2016 at 09:43:24AM +0100, Jiri Slaby wrote:
>>> Hi,
>>>
>>> I can relatively easily reproduce this bug:
> 
> How?

Run dmesg -w in the qemu window (virtio_gpu) to see a lot of output.
Run pps [1] without exit(0); on e.g. serial console.
Wait a bit. The lot of output causes the BUG.

[1] https://github.com/jirislaby/collected_sources/blob/master/pps.c

>>> BUG: 'list_empty(&vgdev->free_vbufs)' is true!
> 
>> The following might be helpful for debugging - if kernel still will
>> not stop panicing, we are looking at some kind
>> of memory corruption.
> 
> Looking carefully through the code I think it isn't impossible to
> trigger this, but you need for that:
> 
>   (1) command queue full (quite possible),
>   (2) cursor queue full too (unlikely), and
>   (3) multiple threads trying to submit commands and waiting for free
>       space in the command queue (possible with virgl enabled).

I use -vga virtio with no -display option, so no virtgl, I suppose:
[drm] virgl 3d acceleration not available

> Do things improve if you allocate some extra bufs?
> 
>  int virtio_gpu_alloc_vbufs(struct virtio_gpu_device *vgdev)
>  {
>         struct virtio_gpu_vbuffer *vbuf;
> -       int i, size, count = 0;
> +       int i, size, count = 16;

This seems to help.

thanks,
-- 
js
suse labs