Re: [PATCH 1/8] soundwire: fix enumeration completion

Pierre-Louis Bossart
2023-07-05T13:58:09Z

On 7/5/23 14:30, Johan Hovold wrote:
> The soundwire subsystem uses two completion structures that allow
> drivers to wait for soundwire device to become enumerated on the bus and
> initialised by their drivers, respectively.
>
> The code implementing the signalling is currently broken as it does not
> signal all current and future waiters and also uses the wrong
> reinitialisation function, which can potentially lead to memory
> corruption if there are still waiters on the queue.

That change sounds good, but I am not following the two paragraphs below.

> Not signalling future waiters specifically breaks sound card probe
> deferrals as codec drivers can not tell that the soundwire device is
> already attached when being reprobed.

What makes you say that? There is a test in the probe and the codec
driver will absolutely be notified, see bus_type.c

if (drv->ops && drv->ops->update_status) {
ret = drv->ops->update_status(slave, slave->status);
if (ret < 0)
dev_warn(dev, "%s: update_status failed with status %d\n", __func__,
ret);
}

> Some codec runtime PM
> implementations suffer from similar problems as waiting for enumeration
> during resume can also timeout despite the device already having been
> enumerated.

I am not following this either. Are you saying the wait_for_completion()
times out because of the init_completion/reinit_completion confusion, or
something else.

> Fixes: fb9469e54fa7 ("soundwire: bus: fix race condition with enumeration_complete signaling")
> Fixes: a90def068127 ("soundwire: bus: fix race condition with initialization_complete signaling")
> Cc: stable@vger.kernel.org # 5.7
> Cc: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
> Cc: Rander Wang <rander.wang@linux.intel.com>
> Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
> ---
> drivers/soundwire/bus.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c
> index 1ea6a64f8c4a..66e5dba919fa 100644
> --- a/drivers/soundwire/bus.c
> +++ b/drivers/soundwire/bus.c
> @@ -908,8 +908,8 @@ static void sdw_modify_slave_status(struct sdw_slave *slave,
> "initializing enumeration and init completion for Slave %d\n",
> slave->dev_num);
>
> - init_completion(&slave->enumeration_complete);
> - init_completion(&slave->initialization_complete);
> + reinit_completion(&slave->enumeration_complete);
> + reinit_completion(&slave->initialization_complete);
>
> } else if ((status == SDW_SLAVE_ATTACHED) &&
> (slave->status == SDW_SLAVE_UNATTACHED)) {
> @@ -917,7 +917,7 @@ static void sdw_modify_slave_status(struct sdw_slave *slave,
> "signaling enumeration completion for Slave %d\n",
> slave->dev_num);
>
> - complete(&slave->enumeration_complete);
> + complete_all(&slave->enumeration_complete);
> }
> slave->status = status;
> mutex_unlock(&bus->bus_lock);
> @@ -1941,7 +1941,7 @@ int sdw_handle_slave_status(struct sdw_bus *bus,
> "signaling initialization completion for Slave %d\n",
> slave->dev_num);
>
> - complete(&slave->initialization_complete);
> + complete_all(&slave->initialization_complete);
>
> /*
> * If the manager became pm_runtime active, the peripherals will be