[PATCH 2/2] hwmon: (lm90) Add lock protection to lm90_alert

[Guenter Roeck <linux@roeck-us.net>]

Sashiko reports:

lm90_alert() executes in the smbus alert context and calls
lm90_update_confreg() to disable the hardware alert line, without
acquiring hwmon_lock.

Concurrently, sysfs write operations (such as lm90_write_convrate) hold
the hwmon_lock, temporarily modify data->config, and then restore it.

If an alert interrupt occurs concurrently with a sysfs write, the sysfs
path will overwrite the alert handler's modifications to data->config
and the hardware register.

This unintentionally re-enables the hardware alert line while the alarm is
still active, causing an interrupt storm.

Add the missing lock to lm90_alert() to solve the problem.

Fixes: 7a1d220ccb0cc ("hwmon: (lm90) Introduce function to update configuration register")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 drivers/hwmon/lm90.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/hwmon/lm90.c b/drivers/hwmon/lm90.c
index 50b30d719225..6658c743659b 100644
--- a/drivers/hwmon/lm90.c
+++ b/drivers/hwmon/lm90.c
@@ -2939,6 +2939,7 @@ static void lm90_alert(struct i2c_client *client, enum i2c_alert_protocol type,
 		 */
 		struct lm90_data *data = i2c_get_clientdata(client);
 
+		hwmon_lock(data->hwmon_dev);
 		if ((data->flags & LM90_HAVE_BROKEN_ALERT) &&
 		    (data->current_alarms & data->alert_alarms)) {
 			if (!(data->config & 0x80)) {
@@ -2948,6 +2949,7 @@ static void lm90_alert(struct i2c_client *client, enum i2c_alert_protocol type,
 			schedule_delayed_work(&data->alert_work,
 				max_t(int, HZ, msecs_to_jiffies(data->update_interval)));
 		}
+		hwmon_unlock(data->hwmon_dev);
 	} else {
 		dev_dbg(&client->dev, "Everything OK\n");
 	}
-- 
2.45.2