linux-kernel - Re: [PATCH] virtio_console: allocate inbufs in add

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Message-ID: <ac1cad60-dd5e-532a-8a35-a8dfa2a586a0@redhat.com>
Date:   Wed, 6 Nov 2019 14:53:06 +0100
From:   Laurent Vivier <lvivier@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Amit Shah <amit@...nel.org>,
        virtualization@...ts.linux-foundation.org,
        Arnd Bergmann <arnd@...db.de>,
        "Michael S . Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH] virtio_console: allocate inbufs in add_port() only if it
 is needed

Any comments?

Thanks,
Laurent

On 18/10/2019 18:47, 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 only allocate the
> buffers if the in_vq has available free slots.
> 
> Fixes: a7a69ec0d8e4 ("virtio_console: free buffers after reset")
> Cc: mst@...hat.com
> Signed-off-by: Laurent Vivier <lvivier@...hat.com>
> ---
>  drivers/char/virtio_console.c | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> index 7270e7b69262..77105166fe01 100644
> --- a/drivers/char/virtio_console.c
> +++ b/drivers/char/virtio_console.c
> @@ -1421,12 +1421,17 @@ 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) {
> -		dev_err(port->dev, "Error allocating inbufs\n");
> -		err = -ENOMEM;
> -		goto free_device;
> +	/* if the in_vq has not already been filled (the port has already been
> +	 * used and unplugged), fill the in_vq with buffers so the host can
> +	 * send us data.
> +	 */
> +	if (port->in_vq->num_free != 0) {
> +		nr_added_bufs = fill_queue(port->in_vq, &port->inbuf_lock);
> +		if (!nr_added_bufs) {
> +			dev_err(port->dev, "Error allocating inbufs\n");
> +			err = -ENOMEM;
> +			goto free_device;
> +		}
>  	}
>  
>  	if (is_rproc_serial(port->portdev->vdev))
>