Re: [PATCH v3 07/25] ASoC: qcom: qdsp6: Add support to Q6ADM

Mark Brown
2018-03-01T21:24:23Z

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On Tue, Feb 13, 2018 at 04:58:19PM +0000, srinivas.kandagatla@linaro.org wrote:

> +static struct copp *adm_find_copp(struct q6adm *adm, int port_idx,
> + int copp_idx)
> +{
> + struct copp *c;
> +
> + spin_lock(&adm->copps_list_lock);
> + list_for_each_entry(c, &adm->copps_list, node) {
> + if ((port_idx == c->afe_port) && (copp_idx == c->copp_idx)) {
> + spin_unlock(&adm->copps_list_lock);
> + return c;
> + }
> + }
> +
> + spin_unlock(&adm->copps_list_lock);

We've again got this use of spinlocks here but no IRQ safety - what
exactly is going on with the locking? In general all of the locking in
this stuff is raising very serious alarm bells with me, I don't
understand what is being protected against what and there's some very
obvious bugs. We could probably use some documentation about what the
locking is supposed to be doing.

> + case ADM_CMDRSP_DEVICE_OPEN_V5: {

> + copp->id = open->copp_id;
> + wake_up(&copp->wait);
> + }
> + break;
> + default:

This indentation is confusing.

> +static struct copp *adm_find_matching_copp(struct q6adm *adm,
> + int port_id, int topology,
> + int mode, int rate, int channel_mode,
> + int bit_width, int app_type)
> +{
> + struct copp *c;
> +
> + spin_lock(&adm->copps_list_lock);
> +
> + list_for_each_entry(c, &adm->copps_list, node) {
> + if ((port_id == c->afe_port) && (topology == c->topology) &&
> + (mode == c->mode) && (rate == c->rate) &&
> + (bit_width == c->bit_width) && (app_type == c->app_type)) {
> + spin_unlock(&adm->copps_list_lock);
> + return c;
> + }
> + }
> + spin_unlock(&adm->copps_list_lock);
> +
> + c = adm_alloc_copp(adm, port_id);

So really this is a find or allocate operation...

> + if (IS_ERR_OR_NULL(c))
> + return ERR_CAST(c);
> +
> + mutex_lock(&c->lock);
> + c->refcnt = 0;

Why do we need to lock the thing we just allocated but didn't yet
initialize, and surely if something can find it before we finished
initializing we have a race condition?

> + copp = adm_find_matching_copp(adm, port_id, topology, perf_mode,
> + rate, channel_mode, bit_width, app_type);
> +
> + /* Create a COPP if port id are not enabled */
> + if (copp->refcnt == 0) {
> + ret = q6adm_device_open(adm, copp, port_id, path, topology,
> + channel_mode, bit_width, rate);
> + if (ret < 0)
> + return ret;
> + }
> + mutex_lock(&copp->lock);
> + copp->refcnt++;
> + mutex_unlock(&copp->lock);

There's an obvious race here between checking the reference count and
incrementing it - something might drop a reference before we increment
it which would be bad. I'm also not clear when we'd want multiple
things using a single COPP.

> + mutex_lock(&copp->lock);
> + copp->refcnt--;
> + mutex_unlock(&copp->lock);
> + if (!copp->refcnt) {

This locking is also broken.

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