[alsa-devel] Applied "ASoC: max98090: fix possible race conditions" to the asoc tree

[Mark Brown]

The patch

   ASoC: max98090: fix possible race conditions

has been applied to the asoc tree at

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound.git for-5.5

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 45dfbf56975994822cce00b7475732a49f8aefed Mon Sep 17 00:00:00 2001
From: Tzung-Bi Shih <tzungbi at google.com>
Date: Fri, 22 Nov 2019 15:31:14 +0800
Subject: [PATCH] ASoC: max98090: fix possible race conditions

max98090_interrupt() and max98090_pll_work() run in 2 different threads.
There are 2 possible races:

Note: M98090_REG_DEVICE_STATUS = 0x01.
Note: ULK == 0, PLL is locked; ULK == 1, PLL is unlocked.

max98090_interrupt      max98090_pll_work
----------------------------------------------
schedule max98090_pll_work
                        restart max98090 codec
receive ULK INT
                        assert ULK == 0
schedule max98090_pll_work (1).

In the case (1), the PLL is locked but max98090_interrupt unnecessarily
schedules another max98090_pll_work.

max98090_interrupt      max98090_pll_work      max98090 codec
----------------------------------------------------------------------
                                               ULK = 1
receive ULK INT
read 0x01
                                               ULK = 0 (clear on read)
schedule max98090_pll_work
                        restart max98090 codec
                                               ULK = 1
receive ULK INT
read 0x01
                                               ULK = 0 (clear on read)
                        read 0x01
                        assert ULK == 0 (2).

In the case (2), both max98090_interrupt and max98090_pll_work read
the same clear-on-read register.  max98090_pll_work would falsely
thought PLL is locked.
Note: the case (2) race is introduced by the previous commit ("ASoC:
max98090: exit workaround earlier if PLL is locked") to check the status
and exit the loop earlier in max98090_pll_work.

There are 2 possible solution options:
A. turn off ULK interrupt before scheduling max98090_pll_work; and turn
on again before exiting max98090_pll_work.
B. remove the second thread of execution.

Option A cannot fix the case (2) race because it still has 2 threads
access the same clear-on-read register simultaneously.  Although we
could suppose the register is volatile and read the status via I2C could
be much slower than the hardware raises the bits.

Option B introduces a maximum 10~12 msec penalty delay in the interrupt
handler.  However, it could only punish the jack detection by extra
10~12 msec.

Adopts option B which is the better solution overall.

Signed-off-by: Tzung-Bi Shih <tzungbi at google.com>
Link: https://lore.kernel.org/r/20191122073114.219945-4-tzungbi@google.com
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
Signed-off-by: Mark Brown <broonie at kernel.org>
---
 sound/soc/codecs/max98090.c | 8 ++------
 sound/soc/codecs/max98090.h | 1 -
 2 files changed, 2 insertions(+), 7 deletions(-)

diff --git a/sound/soc/codecs/max98090.c b/sound/soc/codecs/max98090.c
index f531e5a11bdd..e46b6ada13b1 100644
--- a/sound/soc/codecs/max98090.c
+++ b/sound/soc/codecs/max98090.c
@@ -2103,10 +2103,8 @@ static void max98090_pll_det_disable_work(struct work_struct *work)
 			    M98090_IULK_MASK, 0);
 }
 
-static void max98090_pll_work(struct work_struct *work)
+static void max98090_pll_work(struct max98090_priv *max98090)
 {
-	struct max98090_priv *max98090 =
-		container_of(work, struct max98090_priv, pll_work);
 	struct snd_soc_component *component = max98090->component;
 	unsigned int pll;
 	int i;
@@ -2275,7 +2273,7 @@ static irqreturn_t max98090_interrupt(int irq, void *data)
 
 	if (active & M98090_ULK_MASK) {
 		dev_dbg(component->dev, "M98090_ULK_MASK\n");
-		schedule_work(&max98090->pll_work);
+		max98090_pll_work(max98090);
 	}
 
 	if (active & M98090_JDET_MASK) {
@@ -2438,7 +2436,6 @@ static int max98090_probe(struct snd_soc_component *component)
 			  max98090_pll_det_enable_work);
 	INIT_WORK(&max98090->pll_det_disable_work,
 		  max98090_pll_det_disable_work);
-	INIT_WORK(&max98090->pll_work, max98090_pll_work);
 
 	/* Enable jack detection */
 	snd_soc_component_write(component, M98090_REG_JACK_DETECT,
@@ -2491,7 +2488,6 @@ static void max98090_remove(struct snd_soc_component *component)
 	cancel_delayed_work_sync(&max98090->jack_work);
 	cancel_delayed_work_sync(&max98090->pll_det_enable_work);
 	cancel_work_sync(&max98090->pll_det_disable_work);
-	cancel_work_sync(&max98090->pll_work);
 	max98090->component = NULL;
 }
 
diff --git a/sound/soc/codecs/max98090.h b/sound/soc/codecs/max98090.h
index 57965cd678b4..a197114b0dad 100644
--- a/sound/soc/codecs/max98090.h
+++ b/sound/soc/codecs/max98090.h
@@ -1530,7 +1530,6 @@ struct max98090_priv {
 	struct delayed_work jack_work;
 	struct delayed_work pll_det_enable_work;
 	struct work_struct pll_det_disable_work;
-	struct work_struct pll_work;
 	struct snd_soc_jack *jack;
 	unsigned int dai_fmt;
 	int tdm_slots;
-- 
2.20.1