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Re: [PATCH v3 2/2] vhost-user-blk: delay vhost_user_blk_disconnect
From: |
Raphael Norwitz |
Subject: |
Re: [PATCH v3 2/2] vhost-user-blk: delay vhost_user_blk_disconnect |
Date: |
Mon, 25 May 2020 00:00:10 -0400 |
I'm mostly happy with this. A couple comments.
On Wed, May 20, 2020 at 11:54 AM Dima Stepanov <address@hidden> 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"
>
I'd also give credit to Li Feng here - he sent a similar patch:
https://lists.gnu.org/archive/html/qemu-devel/2020-04/msg02255.html
> Signed-off-by: Dima Stepanov <address@hidden>
> ---
> 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));
I find checking s->connected before ret a little confusing. I think we
should also enforce a reconnect if s->connected is false. AFIK if
s->connected is false, ret must also be less than 0, but to be safe
I’d prefer something like:
if (ret < 0 || !s->connected) {
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;
}
> + 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;
> --
> 2.7.4
>
>