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

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Date:   Wed, 5 Jul 2023 14:53:17 +0200
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Johan Hovold <johan+linaro@...nel.org>,
        Mark Brown <broonie@...nel.org>, Vinod Koul <vkoul@...nel.org>
Cc:     Bard Liao <yung-chuan.liao@...ux.intel.com>,
        Sanyog Kale <sanyog.r.kale@...el.com>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Banajit Goswami <bgoswami@...cinc.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Rander Wang <rander.wang@...ux.intel.com>
Subject: Re: [PATCH 1/8] soundwire: fix enumeration completion



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@...r.kernel.org      # 5.7
> Cc: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
> Cc: Rander Wang <rander.wang@...ux.intel.com>
> Signed-off-by: Johan Hovold <johan+linaro@...nel.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