linux-kernel - Re: [PATCH] ASoC: atmel_ssc_dai: Remove wrong spinlock usage

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Date:   Wed, 18 Sep 2019 11:48:00 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Gregory CLEMENT <gregory.clement@...tlin.com>
Cc:     Codrin Ciubotariu <codrin.ciubotariu@...rochip.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Ludovic Desroches <ludovic.desroches@...rochip.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] ASoC: atmel_ssc_dai: Remove wrong spinlock usage

On 18/09/2019 11:41:14+0200, Gregory CLEMENT wrote:
> A potential bug was reported in the email "[BUG] atmel_ssc_dai: a
> possible sleep-in-atomic bug in atmel_ssc_shutdown"[1]
> 
> Indeed in the function atmel_ssc_shutdown() free_irq() was called in a
> critical section protected by spinlock.
> 
> However this spinlock is only used in atmel_ssc_shutdown() and
> atmel_ssc_startup() functions. After further analysis, it occurred that
> the call to these function are already protected by mutex used on the
> calling functions.
> 
> Then we can remove the spinlock which will fix this bug as a side
> effect. Thanks to this patch the following message disappears:
> 
> "BUG: sleeping function called from invalid context at
> kernel/locking/mutex.c:909"
> 
> [1]: https://www.spinics.net/lists/alsa-devel/msg71286.html
> 
> Signed-off-by: Gregory CLEMENT <gregory.clement@...tlin.com>
> ---
>  sound/soc/atmel/atmel_ssc_dai.c | 7 -------
>  1 file changed, 7 deletions(-)
> 
> diff --git a/sound/soc/atmel/atmel_ssc_dai.c b/sound/soc/atmel/atmel_ssc_dai.c
> index 6f89483ac88c..365957e86419 100644
> --- a/sound/soc/atmel/atmel_ssc_dai.c
> +++ b/sound/soc/atmel/atmel_ssc_dai.c
> @@ -116,19 +116,16 @@ static struct atmel_pcm_dma_params ssc_dma_params[NUM_SSC_DEVICES][2] = {
>  static struct atmel_ssc_info ssc_info[NUM_SSC_DEVICES] = {
>  	{
>  	.name		= "ssc0",
> -	.lock		= __SPIN_LOCK_UNLOCKED(ssc_info[0].lock),

This member is now unused and can be removed from the struct.

Once fixed, Reviewed-by: Alexandre Belloni <alexandre.belloni@...tlin.com>

>  	.dir_mask	= SSC_DIR_MASK_UNUSED,
>  	.initialized	= 0,
>  	},
>  	{
>  	.name		= "ssc1",
> -	.lock		= __SPIN_LOCK_UNLOCKED(ssc_info[1].lock),
>  	.dir_mask	= SSC_DIR_MASK_UNUSED,
>  	.initialized	= 0,
>  	},
>  	{
>  	.name		= "ssc2",
> -	.lock		= __SPIN_LOCK_UNLOCKED(ssc_info[2].lock),
>  	.dir_mask	= SSC_DIR_MASK_UNUSED,
>  	.initialized	= 0,
>  	},
> @@ -317,13 +314,11 @@ static int atmel_ssc_startup(struct snd_pcm_substream *substream,
>  
>  	snd_soc_dai_set_dma_data(dai, substream, dma_params);
>  
> -	spin_lock_irq(&ssc_p->lock);
>  	if (ssc_p->dir_mask & dir_mask) {
>  		spin_unlock_irq(&ssc_p->lock);
>  		return -EBUSY;
>  	}
>  	ssc_p->dir_mask |= dir_mask;
> -	spin_unlock_irq(&ssc_p->lock);
>  
>  	return 0;
>  }
> @@ -355,7 +350,6 @@ static void atmel_ssc_shutdown(struct snd_pcm_substream *substream,
>  
>  	dir_mask = 1 << dir;
>  
> -	spin_lock_irq(&ssc_p->lock);
>  	ssc_p->dir_mask &= ~dir_mask;
>  	if (!ssc_p->dir_mask) {
>  		if (ssc_p->initialized) {
> @@ -369,7 +363,6 @@ static void atmel_ssc_shutdown(struct snd_pcm_substream *substream,
>  		ssc_p->cmr_div = ssc_p->tcmr_period = ssc_p->rcmr_period = 0;
>  		ssc_p->forced_divider = 0;
>  	}
> -	spin_unlock_irq(&ssc_p->lock);
>  
>  	/* Shutdown the SSC clock. */
>  	pr_debug("atmel_ssc_dai: Stopping clock\n");
> -- 
> 2.23.0
> 

-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com