linux-kernel - Re: [PATCH] drm/virtio: kick vq outside of the vq lock

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Message-ID: <20190802080245.za2n5rgx763xvhpd@sirius.home.kraxel.org>
Date:   Fri, 2 Aug 2019 10:02:45 +0200
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     Chia-I Wu <olvaffe@...il.com>
Cc:     dri-devel@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/virtio: kick vq outside of the vq lock

> @@ -291,11 +291,9 @@ static int virtio_gpu_queue_ctrl_buffer_locked(struct virtio_gpu_device *vgdev,
>  		trace_virtio_gpu_cmd_queue(vq,
>  			(struct virtio_gpu_ctrl_hdr *)vbuf->buf);
>  
> -		virtqueue_kick(vq);
> +		ret = virtqueue_kick_prepare(vq);
>  	}
>  
> -	if (!ret)
> -		ret = vq->num_free;

Hmm.  Change looks unrelated.

On a closer look it seems this is basically dead code.
virtio_gpu_queue_ctrl_buffer_locked is called by
virtio_gpu_queue_ctrl_buffer and virtio_gpu_queue_fenced_ctrl_buffer.
The call sites for these two functions all ignore the return value.

So it is a valid change, but it should go to a separate patch.  And
while being at it virtio_gpu_queue_ctrl_buffer and
virtio_gpu_queue_fenced_ctrl_buffer can be changed to return void.

Otherwise the patch looks fine.  Nice analysis btw.

cheers,
  Gerd