[PATCH v3 10/11] hwmon: chipcap2: serialize access to the alarm indicators

[Javier Carrasco <javier.carrasco.cruz@gmail.com>]

low_alarm and high_alarm are accessed from the threaded interrupt
handlers and from sysfs without any locking, which can lead to lost
alarms.

Add a mutex to serialize the access to the alarm indicators and to
process_irqs, which the handlers use to decide whether an interrupt
belongs to an ongoing operation.

Fixes: 3af350929e75 ("hwmon: Add support for Amphenol ChipCap 2")
Cc: stable@vger.kernel.org
Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Assisted-by: opencode:claude-opus-5
---
 drivers/hwmon/chipcap2.c | 58 ++++++++++++++++++++++++++++++------------------
 1 file changed, 37 insertions(+), 21 deletions(-)

diff --git a/drivers/hwmon/chipcap2.c b/drivers/hwmon/chipcap2.c
index eba6469940ab..b3b725cc7224 100644
--- a/drivers/hwmon/chipcap2.c
+++ b/drivers/hwmon/chipcap2.c
@@ -20,6 +20,7 @@
 #include <linux/i2c.h>
 #include <linux/interrupt.h>
 #include <linux/irq.h>
+#include <linux/mutex.h>
 #include <linux/module.h>
 #include <linux/unaligned.h>
 #include <linux/regulator/consumer.h>
@@ -91,6 +92,8 @@ struct cc2_data {
 	int irq_low;
 	int irq_high;
 	bool process_irqs;
+	/* protects process_irqs and the alarm indicators */
+	struct mutex irq_lock;
 	bool regulator_enabled;
 };
 
@@ -122,7 +125,8 @@ static int cc2_enable(struct cc2_data *data)
 
 	/* exclusive regulator, check in case a disable failed */
 	if (data->regulator_enabled) {
-		data->process_irqs = true;
+		scoped_guard(mutex, &data->irq_lock)
+			data->process_irqs = true;
 		return 0;
 	}
 
@@ -137,7 +141,8 @@ static int cc2_enable(struct cc2_data *data)
 
 	usleep_range(CC2_STARTUP_TIME_US, CC2_STARTUP_TIME_US + 125);
 
-	data->process_irqs = true;
+	scoped_guard(mutex, &data->irq_lock)
+		data->process_irqs = true;
 
 	return 0;
 }
@@ -154,7 +159,8 @@ static void cc2_disable(struct cc2_data *data)
 		synchronize_irq(data->irq_high);
 
 	/* ignore alarms triggered by voltage toggling when powering up */
-	data->process_irqs = false;
+	scoped_guard(mutex, &data->irq_lock)
+		data->process_irqs = false;
 
 	/* exclusive regulator, check in case an enable failed */
 	if (!data->regulator_enabled)
@@ -514,10 +520,12 @@ static irqreturn_t cc2_low_interrupt(int irq, void *data)
 {
 	struct cc2_data *cc2 = data;
 
-	if (cc2->process_irqs) {
-		hwmon_notify_event(cc2->hwmon, hwmon_humidity,
-				   hwmon_humidity_min_alarm, 0);
-		cc2->rh_alarm.low_alarm = true;
+	scoped_guard(mutex, &cc2->irq_lock) {
+		if (cc2->process_irqs) {
+			hwmon_notify_event(cc2->hwmon, hwmon_humidity,
+					   hwmon_humidity_min_alarm, 0);
+			cc2->rh_alarm.low_alarm = true;
+		}
 	}
 
 	return IRQ_HANDLED;
@@ -527,10 +535,12 @@ static irqreturn_t cc2_high_interrupt(int irq, void *data)
 {
 	struct cc2_data *cc2 = data;
 
-	if (cc2->process_irqs) {
-		hwmon_notify_event(cc2->hwmon, hwmon_humidity,
-				   hwmon_humidity_max_alarm, 0);
-		cc2->rh_alarm.high_alarm = true;
+	scoped_guard(mutex, &cc2->irq_lock) {
+		if (cc2->process_irqs) {
+			hwmon_notify_event(cc2->hwmon, hwmon_humidity,
+					   hwmon_humidity_max_alarm, 0);
+			cc2->rh_alarm.high_alarm = true;
+		}
 	}
 
 	return IRQ_HANDLED;
@@ -546,11 +556,13 @@ static int cc2_humidity_min_alarm_status(struct cc2_data *data, long *val)
 	if (ret < 0)
 		return ret;
 
-	if (data->rh_alarm.low_alarm) {
-		*val = (measurement < min_hyst) ? 1 : 0;
-		data->rh_alarm.low_alarm = *val;
-	} else {
-		*val = 0;
+	scoped_guard(mutex, &data->irq_lock) {
+		if (data->rh_alarm.low_alarm) {
+			*val = (measurement < min_hyst) ? 1 : 0;
+			data->rh_alarm.low_alarm = *val;
+		} else {
+			*val = 0;
+		}
 	}
 
 	return 0;
@@ -566,11 +578,13 @@ static int cc2_humidity_max_alarm_status(struct cc2_data *data, long *val)
 	if (ret < 0)
 		return ret;
 
-	if (data->rh_alarm.high_alarm) {
-		*val = (measurement > max_hyst) ? 1 : 0;
-		data->rh_alarm.high_alarm = *val;
-	} else {
-		*val = 0;
+	scoped_guard(mutex, &data->irq_lock) {
+		if (data->rh_alarm.high_alarm) {
+			*val = (measurement > max_hyst) ? 1 : 0;
+			data->rh_alarm.high_alarm = *val;
+		} else {
+			*val = 0;
+		}
 	}
 
 	return 0;
@@ -753,6 +767,8 @@ static int cc2_probe(struct i2c_client *client)
 
 	i2c_set_clientdata(client, data);
 
+	mutex_init(&data->irq_lock);
+
 	data->client = client;
 
 	data->regulator = devm_regulator_get_exclusive(dev, "vdd");

-- 
2.43.0