Re: [PATCH v4 2/2] vhost-user-blk: delay vhost_user_blk_disconnect

[Dima Stepanov <dimastep@yandex-team.ru>]

On Sat, May 30, 2020 at 08:55:30PM -0400, Raphael Norwitz wrote:
> On Thu, May 28, 2020 at 5:13 AM Dima Stepanov <dimastep@yandex-team.ru> 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>
> 
> Reviewed-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
> 
> Li Feng - would you also like to sign off here?
Raphael,

Will you take this patchset for merging or what is the next step? )

Thanks, Dima.

> 
> > ---
> >  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
> >
> >