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

[Jason Wang <jasowang@redhat.com>]

On 2020/5/20 下午11:53, 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"


It's better to explain why we don't need to deal with case 1 in the 
vhost-user-net case.

And do we still need patch 1 if we had this patch??

Thanks


>
> Signed-off-by: Dima Stepanov <dimastep@yandex-team.ru>
> ---
>   hw/block/vhost-user-blk.c | 49 +++++++++++++++++++++++++++++++++++++++++------
>   1 file changed, 43 insertions(+), 6 deletions(-)
>
> diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
> index 9d8c0b3..447fc9c 100644
> --- a/hw/block/vhost-user-blk.c
> +++ b/hw/block/vhost-user-blk.c
> @@ -337,11 +337,6 @@ static void vhost_user_blk_disconnect(DeviceState *dev)
>       VirtIODevice *vdev = VIRTIO_DEVICE(dev);
>       VHostUserBlk *s = VHOST_USER_BLK(vdev);
>   
> -    if (!s->connected) {
> -        return;
> -    }
> -    s->connected = false;
> -
>       if (s->dev.started) {
>           vhost_user_blk_stop(vdev);
>       }
> @@ -349,6 +344,19 @@ 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 +371,28 @@ 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.
> +         */
> +        if (s->connected && 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);
> +        }
> +        s->connected = false;
>           break;
>       case CHR_EVENT_BREAK:
>       case CHR_EVENT_MUX_IN:
> @@ -428,6 +457,14 @@ reconnect:
>   
>       ret = vhost_dev_get_config(&s->dev, (uint8_t *)&s->blkcfg,
>                                  sizeof(struct virtio_blk_config));
> +    if (!s->connected) {
> +        /*
> +         * Perform disconnect before making reconnect. More detailed
> +         * comment why it was delayed is in the vhost_user_blk_event()
> +         * routine.
> +         */
> +        vhost_user_blk_disconnect(dev);
> +    }
>       if (ret < 0) {
>           error_report("vhost-user-blk: get block config failed");
>           goto reconnect;