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SubjectRe: [PATCH v3] virtio_console: allocate inbufs in add_port() only if it is needed
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On Thu, 2019-11-14 at 13:25 +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>

Reviewed-by: Amit Shah <amit@kernel.org>

Thanks!

> ---
>
> Notes:
> v3: add a comment about ENOSPC error
> v2: making fill_queue return int and testing return code for
> -ENOSPC
>
> drivers/char/virtio_console.c | 28 +++++++++++++---------------
> 1 file changed, 13 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/char/virtio_console.c
> b/drivers/char/virtio_console.c
> index 7270e7b69262..3259426f01dc 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 +1420,13 @@ 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) {
> + /* We can safely ignore ENOSPC because it means
> + * the queue already has buffers. Buffers are removed
> + * only by virtcons_remove(), not by unplug_port()
> + */
> + 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;
> }
>
> @@ -2059,14 +2060,11 @@ 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 +2075,7 @@ 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 {
> /*

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