Re: [PATCH 05/10] ALSA: axd: add buffers manipulation files

Mark Brown
2015-08-26T18:43:35Z

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On Mon, Aug 24, 2015 at 01:39:14PM +0100, Qais Yousef wrote:

> + /*
> + * must ensure we have one access at a time to the queue and rd_idx
> + * to be preemption and SMP safe
> + * Sempahores will ensure that we will only read after a complete write
> + * has finished, so we will never read and write from the same location.
> + */

In what way will sempahores ensure that we will only read after a
complete write?

> + buf = bufferq->queue[bufferq->rd_idx];

So buffers are always retired in the same order that they are acquired?

> +int axd_bufferq_put(struct axd_bufferq *bufferq, char *buf, int buf_size)
> +{
> + int ret;
> +
> + if (!bufferq->queue)
> + return 0;
> +
> + if (buf_size < 0)
> + buf_size = bufferq->stride;

We've got strides as well? What is that?

> +void axd_bufferq_abort_take(struct axd_bufferq *bufferq)
> +{
> + if (axd_bufferq_is_empty(bufferq)) {
> + bufferq->abort_take = 1;
> + up(&bufferq->rd_sem);
> + }
> +}
> +
> +void axd_bufferq_abort_put(struct axd_bufferq *bufferq)
> +{
> + if (axd_bufferq_is_full(bufferq)) {
> + bufferq->abort_put = 1;
> + up(&bufferq->wr_sem);
> + }
> +}

These look *incredibly* racy. Why are they here and why are they safe?

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