[PATCH v2] ASoC: atmel_ssc_dai: Remove wrong spinlock usage

[PATCH v2] ASoC: atmel_ssc_dai: Remove wrong spinlock usage

[Gregory CLEMENT]

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

Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
---

Changelog:

v1 -> v2:

   - Removed the spinlock from the atmel_ssc_info struct
   - Added the Reviewed-by flag form Alex

 sound/soc/atmel/atmel_ssc_dai.c | 12 ++----------
 sound/soc/atmel/atmel_ssc_dai.h |  1 -
 2 files changed, 2 insertions(+), 11 deletions(-)

diff --git a/sound/soc/atmel/atmel_ssc_dai.c b/sound/soc/atmel/atmel_ssc_dai.c
index 6f89483ac88c..786b48ae4905 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 +314,10 @@ 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);
+	if (ssc_p->dir_mask & dir_mask)
 		return -EBUSY;
-	}
+
 	ssc_p->dir_mask |= dir_mask;
-	spin_unlock_irq(&ssc_p->lock);
 
 	return 0;
 }
@@ -355,7 +349,6 @@ 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 +362,6 @@ 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");
diff --git a/sound/soc/atmel/atmel_ssc_dai.h b/sound/soc/atmel/atmel_ssc_dai.h
index ae764cb541c7..3470b966e449 100644
--- a/sound/soc/atmel/atmel_ssc_dai.h
+++ b/sound/soc/atmel/atmel_ssc_dai.h
@@ -93,7 +93,6 @@ struct atmel_ssc_state {
 struct atmel_ssc_info {
 	char *name;
 	struct ssc_device *ssc;
-	spinlock_t lock;	/* lock for dir_mask */
 	unsigned short dir_mask;	/* 0=unused, 1=playback, 2=capture */
 	unsigned short initialized;	/* true if SSC has been initialized */
 	unsigned short daifmt;
-- 
2.23.0

Applied "ASoC: atmel_ssc_dai: Remove wrong spinlock usage" to the asoc tree

[Mark Brown]

The patch

   ASoC: atmel_ssc_dai: Remove wrong spinlock usage

has been applied to the asoc tree at

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound.git for-5.4

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.  

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

From 0dce49efc70536a8c3b4bb5354a71b727ba31b80 Mon Sep 17 00:00:00 2001
From: Gregory CLEMENT <gregory.clement@bootlin.com>
Date: Wed, 18 Sep 2019 12:03:44 +0200
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

Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Link: https://lore.kernel.org/r/20190918100344.23629-1-gregory.clement@bootlin.com
Signed-off-by: Mark Brown <broonie@kernel.org>
---
 sound/soc/atmel/atmel_ssc_dai.c | 12 ++----------
 sound/soc/atmel/atmel_ssc_dai.h |  1 -
 2 files changed, 2 insertions(+), 11 deletions(-)

diff --git a/sound/soc/atmel/atmel_ssc_dai.c b/sound/soc/atmel/atmel_ssc_dai.c
index 48e9eef34c0f..ca603397651c 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 +314,10 @@ 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);
+	if (ssc_p->dir_mask & dir_mask)
 		return -EBUSY;
-	}
+
 	ssc_p->dir_mask |= dir_mask;
-	spin_unlock_irq(&ssc_p->lock);
 
 	return 0;
 }
@@ -355,7 +349,6 @@ 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 +362,6 @@ 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");
diff --git a/sound/soc/atmel/atmel_ssc_dai.h b/sound/soc/atmel/atmel_ssc_dai.h
index ae764cb541c7..3470b966e449 100644
--- a/sound/soc/atmel/atmel_ssc_dai.h
+++ b/sound/soc/atmel/atmel_ssc_dai.h
@@ -93,7 +93,6 @@ struct atmel_ssc_state {
 struct atmel_ssc_info {
 	char *name;
 	struct ssc_device *ssc;
-	spinlock_t lock;	/* lock for dir_mask */
 	unsigned short dir_mask;	/* 0=unused, 1=playback, 2=capture */
 	unsigned short initialized;	/* true if SSC has been initialized */
 	unsigned short daifmt;
-- 
2.20.1