Re: [Qemu-devel] [PATCH] dataplane: avoid reentrancy during virtio_blk_data_plane_stop()

[Stefan Hajnoczi <stefanha@gmail.com>]

On Tue, Jan 15, 2013 at 05:19:38PM +0100, Stefan Hajnoczi wrote:
> When dataplane is stopping, the s->vdev->binding->set_host_notifier(...,
> false) call can invoke the virtqueue handler if an ioeventfd
> notification is pending.  This causes hw/virtio-blk.c to invoke
> virtio_blk_data_plane_start() before virtio_blk_data_plane_stop()
> returns!
> 
> The result is that we try to restart dataplane while trying to stop it
> and the following assertion is raised:
> 
>   msix_set_mask_notifier: Assertion `!dev->msix_mask_notifier' failed.
> 
> Although the code was intended to prevent this scenario, the s->started
> boolean isn't enough.  Add s->stopping so that we can postpone clearing
> s->started until we've completely stopped dataplane.
> 
> This way, virtqueue handler calls during virtio_blk_data_plane_stop()
> are ignored.  When dataplane is legitimately started again later we
> already self-kick ourselves to resume processing.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  hw/dataplane/virtio-blk.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)

Applied to my block tree:
https://github.com/stefanha/qemu/commits/block

Stefan