Re: [PATCH v2] virtio_console: allocate inbufs in add_port() only if it is needed

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Nov 13, 2019 at 04:00:56PM +0100, Laurent Vivier wrote:
> When we hot unplug a virtserialport and then try to hot plug again,
> it fails:
> 
> (qemu) chardev-add socket,id=serial0,path=/tmp/serial0,server,nowait
> (qemu) device_add virtserialport,bus=virtio-serial0.0,nr=2,\
>                   chardev=serial0,id=serial0,name=serial0
> (qemu) device_del serial0
> (qemu) device_add virtserialport,bus=virtio-serial0.0,nr=2,\
>                   chardev=serial0,id=serial0,name=serial0
> kernel error:
>   virtio-ports vport2p2: Error allocating inbufs
> qemu error:
>   virtio-serial-bus: Guest failure in adding port 2 for device \
>                      virtio-serial0.0
> 
> This happens because buffers for the in_vq are allocated when the port is
> added but are not released when the port is unplugged.
> 
> They are only released when virtconsole is removed (see a7a69ec0d8e4)
> 
> To avoid the problem and to be symmetric, we could allocate all the buffers
> in init_vqs() as they are released in remove_vqs(), but it sounds like
> a waste of memory.
> 
> Rather than that, this patch changes add_port() logic to ignore ENOSPC
> error in fill_queue(), which means queue has already been filled.
> 
> Fixes: a7a69ec0d8e4 ("virtio_console: free buffers after reset")
> Cc: mst@redhat.com
> Cc: stable@vger.kernel.org
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---
> 
> Notes:
>     v2: making fill_queue return int and testing return code for -ENOSPC
> 
>  drivers/char/virtio_console.c | 24 +++++++++---------------
>  1 file changed, 9 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> index 7270e7b69262..9e6534fd1aa4 100644
> --- a/drivers/char/virtio_console.c
> +++ b/drivers/char/virtio_console.c
> @@ -1325,24 +1325,24 @@ static void set_console_size(struct port *port, u16 rows, u16 cols)
>  	port->cons.ws.ws_col = cols;
>  }
>  
> -static unsigned int fill_queue(struct virtqueue *vq, spinlock_t *lock)
> +static int fill_queue(struct virtqueue *vq, spinlock_t *lock)
>  {
>  	struct port_buffer *buf;
> -	unsigned int nr_added_bufs;
> +	int nr_added_bufs;
>  	int ret;
>  
>  	nr_added_bufs = 0;
>  	do {
>  		buf = alloc_buf(vq->vdev, PAGE_SIZE, 0);
>  		if (!buf)
> -			break;
> +			return -ENOMEM;
>  
>  		spin_lock_irq(lock);
>  		ret = add_inbuf(vq, buf);
>  		if (ret < 0) {
>  			spin_unlock_irq(lock);
>  			free_buf(buf, true);
> -			break;
> +			return ret;
>  		}
>  		nr_added_bufs++;
>  		spin_unlock_irq(lock);
> @@ -1362,7 +1362,6 @@ static int add_port(struct ports_device *portdev, u32 id)
>  	char debugfs_name[16];
>  	struct port *port;
>  	dev_t devt;
> -	unsigned int nr_added_bufs;
>  	int err;
>  
>  	port = kmalloc(sizeof(*port), GFP_KERNEL);
> @@ -1421,11 +1420,9 @@ static int add_port(struct ports_device *portdev, u32 id)
>  	spin_lock_init(&port->outvq_lock);
>  	init_waitqueue_head(&port->waitqueue);
>  
> -	/* Fill the in_vq with buffers so the host can send us data. */
> -	nr_added_bufs = fill_queue(port->in_vq, &port->inbuf_lock);
> -	if (!nr_added_bufs) {
> +	err = fill_queue(port->in_vq, &port->inbuf_lock);
> +	if (err < 0 && err != -ENOSPC) {
>  		dev_err(port->dev, "Error allocating inbufs\n");
> -		err = -ENOMEM;
>  		goto free_device;
>  	}
>  

Pls add a comment explaining that -ENOSPC happens when
queue already has buffers (e.g. from previous detach).


> @@ -2059,14 +2056,11 @@ static int virtcons_probe(struct virtio_device *vdev)
>  	INIT_WORK(&portdev->control_work, &control_work_handler);
>  
>  	if (multiport) {
> -		unsigned int nr_added_bufs;
> -
>  		spin_lock_init(&portdev->c_ivq_lock);
>  		spin_lock_init(&portdev->c_ovq_lock);
>  
> -		nr_added_bufs = fill_queue(portdev->c_ivq,
> -					   &portdev->c_ivq_lock);
> -		if (!nr_added_bufs) {
> +		err = fill_queue(portdev->c_ivq, &portdev->c_ivq_lock);
> +		if (err < 0) {
>  			dev_err(&vdev->dev,
>  				"Error allocating buffers for control queue\n");
>  			/*
> @@ -2077,7 +2071,7 @@ static int virtcons_probe(struct virtio_device *vdev)
>  					   VIRTIO_CONSOLE_DEVICE_READY, 0);
>  			/* Device was functional: we need full cleanup. */
>  			virtcons_remove(vdev);
> -			return -ENOMEM;
> +			return err;
>  		}
>  	} else {
>  		/*
> -- 
> 2.23.0