On Sat, 27 Feb 2021 09:59:50 +0100,
Anton Yakovlev wrote:
>
> --- a/sound/virtio/virtio_card.c
> +++ b/sound/virtio/virtio_card.c
> @@ -11,6 +11,10 @@
>
> #include "virtio_card.h"
>
> +int msg_timeout_ms = MSEC_PER_SEC;
> +module_param(msg_timeout_ms, int, 0644);
> +MODULE_PARM_DESC(msg_timeout_ms, "Message completion timeout in milliseconds");
If it's a global variable, better to set a prefix to make it unique,
and use module_param_named().
And, it should be unsigned int, no? (unless a negative value has any meaning)
Otherwise...
> + if (!msg_timeout_ms) {
> + dev_err(&vdev->dev, "msg_timeout_ms value cannot be zero\n");
> + return -EINVAL;
Here a negative value would pass.
(snip)
> +int virtsnd_ctl_msg_send(struct virtio_snd *snd, struct virtio_snd_msg *msg,
> + struct scatterlist *out_sgs,
> + struct scatterlist *in_sgs, bool nowait)
> +{
> + struct virtio_device *vdev = snd->vdev;
> + struct virtio_snd_queue *queue = virtsnd_control_queue(snd);
> + unsigned int js = msecs_to_jiffies(msg_timeout_ms);
> + struct virtio_snd_hdr *request = virtsnd_ctl_msg_request(msg);
> + struct virtio_snd_hdr *response = virtsnd_ctl_msg_response(msg);
> + unsigned int nouts = 0;
> + unsigned int nins = 0;
> + struct scatterlist *psgs[4];
> + bool notify = false;
> + unsigned long flags;
> + int rc;
> +
> + virtsnd_ctl_msg_ref(msg);
> +
> + /* Set the default status in case the message was canceled. */
> + response->code = cpu_to_le32(VIRTIO_SND_S_IO_ERR);
> +
> + psgs[nouts++] = &msg->sg_request;
> + if (out_sgs)
> + psgs[nouts++] = out_sgs;
> +
> + psgs[nouts + nins++] = &msg->sg_response;
> + if (in_sgs)
> + psgs[nouts + nins++] = in_sgs;
> +
> + spin_lock_irqsave(&queue->lock, flags);
> + rc = virtqueue_add_sgs(queue->vqueue, psgs, nouts, nins, msg,
> + GFP_ATOMIC);
It's a bit pity that we have to use GFP_ATOMIC always here...
As long as it's in spinlock, it's the only way.
However, this reminds me of another question: may the virtio event be
handled in an atomic context, e.g. the period elapsed or xrun events?
If so, the current implementation with non-atomic PCM mode is wrong.
Since the non-atomic PCM uses mutex instead of spinlock, it'll lead to
a sleep-in-atomic in snd_pcm_period_elapsed() handling.
I suggested the non-atomic PCM *iff* the all contexts are sleepable;
then the sync can be done in each callback, which makes the code much
simpler usually. But you've already implemented the sync via
sync_stop call, hence the non-atomic PCM has little benefit by its
own.
thanks,
Takashi
