On 06/11/2019 16:03, Michael S. Tsirkin wrote:
> On Wed, Nov 06, 2019 at 03:02:25PM +0100, Laurent Vivier wrote:
>> On 06/11/2019 14:56, Michael S. Tsirkin wrote:
>>> On Fri, Oct 18, 2019 at 06:47:18PM +0200, 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@xxxxxxxxxx
>>>> Signed-off-by: Laurent Vivier <lvivier@xxxxxxxxxx>
>>>> ---
>>>> 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))
>>>
>>> Well fill_queue will just add slots as long as it can.
>>> So on a full queue it does nothing. How does this patch help?
>>
>> Yes, but in this case it returns 0 and so add_port() fails and exits
>> with -ENOMEM and the device is freed. It's what this patch tries to avoid.
>>
>> Thanks,
>> Laurent
>
> Oh I see. However it's a bit asymmetrical to special case ring full.
> How about making fill_queue return int and testing return code for
> -ENOSPC instead? Will also help propagate errors correctly.
Good idea. I'm going to propose a new patch.
> And I guess CC stable?
Sure.
Thanks,
Laurent
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