linux-kernel - Re: [PATCH] ASoC: ti: davinci-mcasp: Fix race condition during probe

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Date: Thu, 18 Apr 2024 12:14:15 +0530
From: Jai Luthra <j-luthra@...com>
To: Joao Paulo Goncalves <jpaulo.silvagoncalves@...il.com>
CC: Peter Ujfalusi <peter.ujfalusi@...il.com>,
        Liam Girdwood
	<lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela
	<perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
        Joao Paulo Goncalves
	<joao.goncalves@...adex.com>,
        <alsa-devel@...a-project.org>, <linux-sound@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>
Subject: Re: [PATCH] ASoC: ti: davinci-mcasp: Fix race condition during probe

Hi Joao,

On Apr 17, 2024 at 15:41:38 -0300, Joao Paulo Goncalves wrote:
> From: Joao Paulo Goncalves <joao.goncalves@...adex.com>
> 
> When using davinci-mcasp as CPU DAI with simple-card, there are some
> conditions that cause simple-card to finish registering a sound card before
> davinci-mcasp finishes registering all sound components. This creates a
> non-working sound card from userspace with no problem indication apart
> from not being able to play/record audio on a PCM stream. The issue
> arises during simultaneous probe execution of both drivers. Specifically,
> the simple-card driver, awaiting a CPU DAI, proceeds as soon as
> davinci-mcasp registers its DAI. However, this process can lead to the
> client mutex lock (client_mutex in soc-core.c) being held or davinci-mcasp
> being preempted before PCM DMA registration on davinci-mcasp finishes.
> This situation occurs when the probes of both drivers run concurrently.
> Below is the code path for this condition. To solve the issue, defer
> davinci-mcasp CPU DAI registration to the last step in the audio part of
> it. This way, simple-card CPU DAI parsing will be deferred until all
> audio components are registered.

Good catch, thanks for the fix.

Reviewed-by: Jai Luthra <j-luthra@...com>

> 
> Fail Code Path:
> 
> simple-card.c: probe starts
> simple-card.c: simple_dai_link_of: simple_parse_node(..,cpu,..) returns EPROBE_DEFER, no CPU DAI yet
> davinci-mcasp.c: probe starts
> davinci-mcasp.c: devm_snd_soc_register_component() register CPU DAI
> simple-card.c: probes again, finish CPU DAI parsing and call devm_snd_soc_register_card()
> simple-card.c: finish probe
> davinci-mcasp.c: *dma_pcm_platform_register() register PCM  DMA
> davinci-mcasp.c: probe finish
> 
> Cc: stable@...r.kernel.org
> Fixes: 9fbd58cf4ab0 ("ASoC: davinci-mcasp: Choose PCM driver based on configured DMA controller")
> Signed-off-by: Joao Paulo Goncalves <joao.goncalves@...adex.com>
> ---
>  sound/soc/ti/davinci-mcasp.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/sound/soc/ti/davinci-mcasp.c b/sound/soc/ti/davinci-mcasp.c
> index b892d66f78470..1e760c3155213 100644
> --- a/sound/soc/ti/davinci-mcasp.c
> +++ b/sound/soc/ti/davinci-mcasp.c
> @@ -2417,12 +2417,6 @@ static int davinci_mcasp_probe(struct platform_device *pdev)
>  
>  	mcasp_reparent_fck(pdev);
>  
> -	ret = devm_snd_soc_register_component(&pdev->dev, &davinci_mcasp_component,
> -					      &davinci_mcasp_dai[mcasp->op_mode], 1);
> -
> -	if (ret != 0)
> -		goto err;
> -
>  	ret = davinci_mcasp_get_dma_type(mcasp);
>  	switch (ret) {
>  	case PCM_EDMA:
> @@ -2449,6 +2443,12 @@ static int davinci_mcasp_probe(struct platform_device *pdev)
>  		goto err;
>  	}
>  
> +	ret = devm_snd_soc_register_component(&pdev->dev, &davinci_mcasp_component,
> +					      &davinci_mcasp_dai[mcasp->op_mode], 1);
> +
> +	if (ret != 0)
> +		goto err;
> +
>  no_audio:
>  	ret = davinci_mcasp_init_gpiochip(mcasp);
>  	if (ret) {
> -- 
> 2.34.1
> 

-- 
Thanks,
Jai

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