[PATCH] hwmon: chipcap2: serialize access to low/high_alarm indicators

[Javier Carrasco]

Access to low_alarm and high_alarm from the threaded interrupt handlers
and sysfs is not protected by any locking mechanism at the moment, which
can lead to missed events.

Add a per-interrupt mutex as the two alarm indicators are completely
independent.

Fixes: 3af350929e75 ("hwmon: Add support for Amphenol ChipCap 2")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Javier Carrasco <javier.carrasco.cruz@xxxxxxxxx>
---
This issue was found by Sashiko[1] when an unrelated patch affected
chipcap2.c. The issue is real as the access to the variables is not
protected by any locking mechanism although 2 different sources
(threaded interrupts and sysfs) could modify them.

The fix has been validated on real hardware with an Amphenol
ChipCap 2 CC2D23S sensor.

Link: [1] https://lore.kernel.org/linux-hwmon/20260625162114.417EA1F000E9@xxxxxxxxxxxxxxx/
---
 drivers/hwmon/chipcap2.c | 38 ++++++++++++++++++++++++++++----------
 1 file changed, 28 insertions(+), 10 deletions(-)

diff --git a/drivers/hwmon/chipcap2.c b/drivers/hwmon/chipcap2.c
index 086571d556b7..1bb4ec96514e 100644
--- a/drivers/hwmon/chipcap2.c
+++ b/drivers/hwmon/chipcap2.c
@@ -73,7 +73,11 @@
 
 struct cc2_rh_alarm_info {
 	bool low_alarm;
+	/* Serialize accesses to low_alarm from threaded IRQ and sysfs */
+	struct mutex low_alarm_lock;
 	bool high_alarm;
+	/* Serialize accesses to high_alarm from threaded IRQ and sysfs */
+	struct mutex high_alarm_lock;
 	bool low_alarm_visible;
 	bool high_alarm_visible;
 };
@@ -500,6 +504,7 @@ static irqreturn_t cc2_low_interrupt(int irq, void *data)
 	if (cc2->process_irqs) {
 		hwmon_notify_event(cc2->hwmon, hwmon_humidity,
 				   hwmon_humidity_min_alarm, CC2_CHAN_HUMIDITY);
+		guard(mutex)(&cc2->rh_alarm.low_alarm_lock);
 		cc2->rh_alarm.low_alarm = true;
 	}
 
@@ -513,6 +518,7 @@ static irqreturn_t cc2_high_interrupt(int irq, void *data)
 	if (cc2->process_irqs) {
 		hwmon_notify_event(cc2->hwmon, hwmon_humidity,
 				   hwmon_humidity_max_alarm, CC2_CHAN_HUMIDITY);
+		guard(mutex)(&cc2->rh_alarm.high_alarm_lock);
 		cc2->rh_alarm.high_alarm = true;
 	}
 
@@ -529,11 +535,13 @@ 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->rh_alarm.low_alarm_lock) {
+		if (data->rh_alarm.low_alarm) {
+			*val = (measurement < min_hyst) ? 1 : 0;
+			data->rh_alarm.low_alarm = *val;
+		} else {
+			*val = 0;
+		}
 	}
 
 	return 0;
@@ -549,11 +557,13 @@ 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->rh_alarm.high_alarm_lock) {
+		if (data->rh_alarm.high_alarm) {
+			*val = (measurement > max_hyst) ? 1 : 0;
+			data->rh_alarm.high_alarm = *val;
+		} else {
+			*val = 0;
+		}
 	}
 
 	return 0;
@@ -720,6 +730,14 @@ static int cc2_probe(struct i2c_client *client)
 	if (!data)
 		return -ENOMEM;
 
+	ret = devm_mutex_init(dev, &data->rh_alarm.low_alarm_lock);
+	if (ret)
+		return ret;
+
+	ret = devm_mutex_init(dev, &data->rh_alarm.high_alarm_lock);
+	if (ret)
+		return ret;
+
 	i2c_set_clientdata(client, data);
 
 	data->client = client;

---
base-commit: 818bebeb63dd6bf5f4e07e145f6cdbace520a34c
change-id: 20260820-chipcap2_locks-c01013a24a0c

Best regards,
-- 
Javier Carrasco <javier.carrasco.cruz@xxxxxxxxx>