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

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?