linux-kernel - Re: [PATCH] virtio_console: free unused buffers with virtio port

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Date:   Mon, 4 Mar 2019 14:25:31 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Pankaj Gupta <pagupta@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, amit@...nel.org,
        arnd@...db.de, gregkh@...uxfoundation.org, xiaohli@...hat.com
Subject: Re: [PATCH] virtio_console: free unused buffers with virtio port

On Mon, Mar 04, 2019 at 06:35:11PM +0530, Pankaj Gupta wrote:
>   The commit a7a69ec0d8e4 ("virtio_console: free buffers after reset")
>   deffered detaching of unused buffer to virtio device unplug time. 
> 
>   This causes unplug/replug of single port in virtio device with an 
>   error "Error allocating inbufs\n". As we don't free the unused buffers 
>   attached with the port. Re-plug the same port tries to allocate new
>   buffers in virtqueue and results in this error if queue is full. 
> 
>   This patch removes the unused buffers in vq's when we unplug the port.
>   This is the best we can do as we cannot call device_reset because virtio 
>   device is still active. This was the working behaviour before the change 
>   introduced in commit b3258ff1d6.
> 
>   Reported-by: Xiaohui Li <xiaohli@...hat.com>
>   Fixes: b3258ff1d6 ("virtio_console: free buffers after reset")
>   Signed-off-by: Pankaj Gupta <pagupta@...hat.com>

I think if you do this you need to add support
in the packed ring.

> ---
>  drivers/char/virtio_console.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> index fbeb71953526..5fbf2ac73111 100644
> --- a/drivers/char/virtio_console.c
> +++ b/drivers/char/virtio_console.c
> @@ -1506,15 +1506,25 @@ static void remove_port(struct kref *kref)
>  	kfree(port);
>  }
>  
> +static void remove_unused_bufs(struct virtqueue *vq)
> +{
> +	struct port_buffer *buf;
> +
> +	while ((buf = virtqueue_detach_unused_buf(vq)))
> +		free_buf(buf, true);
> +}
> +
>  static void remove_port_data(struct port *port)
>  {
>  	spin_lock_irq(&port->inbuf_lock);
>  	/* Remove unused data this port might have received. */
>  	discard_port_data(port);
> +	remove_unused_bufs(port->in_vq);
>  	spin_unlock_irq(&port->inbuf_lock);
>  
>  	spin_lock_irq(&port->outvq_lock);
>  	reclaim_consumed_buffers(port);
> +	remove_unused_bufs(port->out_vq);
>  	spin_unlock_irq(&port->outvq_lock);
>  }
>  
> @@ -1950,11 +1960,9 @@ static void remove_vqs(struct ports_device *portdev)
>  	struct virtqueue *vq;
>  
>  	virtio_device_for_each_vq(portdev->vdev, vq) {
> -		struct port_buffer *buf;
>  
>  		flush_bufs(vq, true);
> -		while ((buf = virtqueue_detach_unused_buf(vq)))
> -			free_buf(buf, true);
> +		remove_unused_bufs(vq);
>  	}
>  	portdev->vdev->config->del_vqs(portdev->vdev);
>  	kfree(portdev->in_vqs);
> -- 
> 2.20.1