Re: [PATCH v4 07/14] ASoC: SOF: Add DSP firmware logger support

[Takashi Iwai <tiwai@suse.de>]

On Wed, 13 Feb 2019 23:07:27 +0100,
Pierre-Louis Bossart wrote:
> 
> +static size_t sof_wait_trace_avail(struct snd_sof_dev *sdev,
> +				   loff_t pos, size_t buffer_size)
> +{
> +	wait_queue_entry_t wait;
> +
> +	/*
> +	 * If host offset is less than local pos, it means write pointer of
> +	 * host DMA buffer has been wrapped. We should output the trace data
> +	 * at the end of host DMA buffer at first.
> +	 */
> +	if (sdev->host_offset < pos)
> +		return buffer_size - pos;
> +
> +	/* If there is available trace data now, it is unnecessary to wait. */
> +	if (sdev->host_offset > pos)
> +		return sdev->host_offset - pos;
> +
> +	/* wait for available trace data from FW */
> +	init_waitqueue_entry(&wait, current);
> +	set_current_state(TASK_INTERRUPTIBLE);
> +	add_wait_queue(&sdev->trace_sleep, &wait);
> +
> +	if (signal_pending(current)) {
> +		remove_wait_queue(&sdev->trace_sleep, &wait);
> +	} else {
> +		/* set timeout to max value, no error code */
> +		schedule_timeout(MAX_SCHEDULE_TIMEOUT);
> +		remove_wait_queue(&sdev->trace_sleep, &wait);
> +	}

Can be slightly optimized here, e.g. no need of two
remove_wait_queue() calls.

> +
> +	/* return bytes available for copy */
> +	if (sdev->host_offset < pos)
> +		return buffer_size - pos;
> +
> +	return sdev->host_offset - pos;

Are these sdev->host_offset accesses race-free?

If I understand correctly, snd_sof_trace_update_pos() can be called at
any time, and the offset might become inconsistent during these
multiple references.


thanks,

Takashi