Re: [PATCH v3 2/2] vhost-user-blk: delay vhost_user_blk_disconnect

[Raphael Norwitz <raphael.s.norwitz@gmail.com>]

On Mon, May 25, 2020 at 4:58 AM Dima Stepanov <dimastep@yandex-team.ru> wrote:
>
> On Wed, May 20, 2020 at 06:53:13PM +0300, Dima Stepanov wrote:
> > A socket write during vhost-user communication may trigger a disconnect
> > event, calling vhost_user_blk_disconnect() and clearing all the
> > vhost_dev structures holding data that vhost-user functions expect to
> > remain valid to roll back initialization correctly. Delay the cleanup to
> > keep vhost_dev structure valid.
> > There are two possible states to handle:
> > 1. RUN_STATE_PRELAUNCH: skip bh oneshot call and perform disconnect in
> > the caller routine.
> > 2. RUN_STATE_RUNNING: delay by using bh
> >
> > BH changes are based on the similar changes for the vhost-user-net
> > device:
> >   commit e7c83a885f865128ae3cf1946f8cb538b63cbfba
> >   "vhost-user: delay vhost_user_stop"
> >
> > Signed-off-by: Dima Stepanov <dimastep@yandex-team.ru>
>
> I've reworked the patch based on Raphael's comment and send it for
> review. Also i added a TODO comment in the vhost_user_blk_event()
> routine. After review i'll send a v4 patch set.

Looks good to me.

>
> ---
>  hw/block/vhost-user-blk.c | 38 +++++++++++++++++++++++++++++++++++++-
>  1 file changed, 37 insertions(+), 1 deletion(-)
>
> diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
> index 9d8c0b3..76838e7 100644
> --- a/hw/block/vhost-user-blk.c
> +++ b/hw/block/vhost-user-blk.c
> @@ -349,6 +349,19 @@ static void vhost_user_blk_disconnect(DeviceState *dev)
>      vhost_dev_cleanup(&s->dev);
>  }
>
> +static void vhost_user_blk_event(void *opaque, QEMUChrEvent event);
> +
> +static void vhost_user_blk_chr_closed_bh(void *opaque)
> +{
> +    DeviceState *dev = opaque;
> +    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> +    VHostUserBlk *s = VHOST_USER_BLK(vdev);
> +
> +    vhost_user_blk_disconnect(dev);
> +    qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL, vhost_user_blk_event,
> +            NULL, opaque, NULL, true);
> +}
> +
>  static void vhost_user_blk_event(void *opaque, QEMUChrEvent event)
>  {
>      DeviceState *dev = opaque;
> @@ -363,7 +376,30 @@ static void vhost_user_blk_event(void *opaque, QEMUChrEvent event)
>          }
>          break;
>      case CHR_EVENT_CLOSED:
> -        vhost_user_blk_disconnect(dev);
> +        /*
> +         * A close event may happen during a read/write, but vhost
> +         * code assumes the vhost_dev remains setup, so delay the
> +         * stop & clear. There are two possible paths to hit this
> +         * disconnect event:
> +         * 1. When VM is in the RUN_STATE_PRELAUNCH state. The
> +         * vhost_user_blk_device_realize() is a caller.
> +         * 2. In tha main loop phase after VM start.
> +         *
> +         * For p2 the disconnect event will be delayed. We can't
> +         * do the same for p1, because we are not running the loop
> +         * at this moment. So just skip this step and perform
> +         * disconnect in the caller function.
> +         *
> +         * TODO: maybe it is a good idea to make the same fix
> +         * for other vhost-user devices.
> +         */
> +        if (runstate_is_running()) {
> +            AioContext *ctx = qemu_get_current_aio_context();
> +
> +            qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL, NULL, NULL,
> +                    NULL, NULL, false);
> +            aio_bh_schedule_oneshot(ctx, vhost_user_blk_chr_closed_bh, opaque);
> +        }
>          break;
>      case CHR_EVENT_BREAK:
>      case CHR_EVENT_MUX_IN:
> --
> 2.7.4
>
>