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

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Message-Id: <20190918094114.15867-1-gregory.clement@bootlin.com>
Date:   Wed, 18 Sep 2019 11:41:14 +0200
From:   Gregory CLEMENT <gregory.clement@...tlin.com>
To:     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
Cc:     Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Ludovic Desroches <ludovic.desroches@...rochip.com>,
        linux-arm-kernel@...ts.infradead.org,
        Gregory CLEMENT <gregory.clement@...tlin.com>
Subject: [PATCH] ASoC: atmel_ssc_dai: Remove wrong spinlock usage

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),
 	.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