[Qemu-devel] [Bug 1784900] Re: QEMU (frontend) crashes upon warm reboot with virtio-gpu device and vga=775 on Linux cmdline

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

I also hit this with gtk frontend rather than vnc althought he backtrace
looks very different.

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https://bugs.launchpad.net/bugs/1784900

Title:
  QEMU (frontend) crashes upon warm reboot with virtio-gpu device and
  vga=775 on Linux cmdline

Status in QEMU:
  New

Bug description:
  With vga=775 on the Linux command line a first boot of the VM running
  Linux works fine. After a warm reboot it crashes during Linux boot.
  The VM was used remotely via virt-manager and VNC.

  Bisecting the code lead to the following patch that introduced the
  bug:

  commit 1fccd7c5a9a722a9cbf1bc91693f4618034f01ac (HEAD, refs/bisect/bad)
  Author: Gerd Hoffmann <kraxel@redhat.com>
  Date:   Mon Jul 2 18:24:43 2018 +0200

      virtio-gpu: disable scanout when backing resource is destroyed

      Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
      Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
      Message-id: 20180702162443.16796-4-kraxel@redhat.com

  diff --git a/hw/display/virtio-gpu.c b/hw/display/virtio-gpu.c
  index 336dc59007..08cd567218 100644
  --- a/hw/display/virtio-gpu.c
  +++ b/hw/display/virtio-gpu.c
  @@ -430,6 +430,16 @@ static void virtio_gpu_disable_scanout(VirtIOGPU *g, int scanout_id)
   static void virtio_gpu_resource_destroy(VirtIOGPU *g,
                                           struct virtio_gpu_simple_resource *res)
   {
  +    int i;
  +
  +    if (res->scanout_bitmask) {
  +        for (i = 0; i < g->conf.max_outputs; i++) {
  +            if (res->scanout_bitmask & (1 << i)) {
  +                virtio_gpu_disable_scanout(g, i);
  +            }
  +        }
  +    }
  +
       pixman_image_unref(res->image);
       virtio_gpu_cleanup_mapping(res);
       QTAILQ_REMOVE(&g->reslist, res, next);

  
  Reported backtraces can be found here:  https://paste.fedoraproject.org/paste/OUDEfCk1IY7xiy0I0PDlkw

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