hwmon: (pmbus/isl68137) Add mutex protection for AVS enable sysfs attributes

The custom avs0_enable and avs1_enable sysfs attributes access PMBus
registers through the exported API helpers (pmbus_read_byte_data,
pmbus_read_word_data, pmbus_write_word_data, pmbus_update_byte_data)
without holding the PMBus update_lock mutex. These exported helpers do
not acquire the mutex internally, unlike the core's internal callers
which hold the lock before invoking them.

The store callback is especially vulnerable: it performs a multi-step
read-modify-write sequence (read VOUT_COMMAND, write VOUT_COMMAND, then
update OPERATION) where concurrent access from another thread could
interleave and corrupt the register state.

Add pmbus_lock_interruptible()/pmbus_unlock() around both the show and
store callbacks to serialize PMBus register access with the rest of the
driver.

Fixes: 038a9c3 ("hwmon: (pmbus/isl68137) Add driver for Intersil ISL68137 PWM Controller")
Cc: [email protected]
Signed-off-by: Sanman Pradhan <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Guenter Roeck <[email protected]>

Author: Sanman Pradhan

drivers/hwmon/pmbus/isl68137.c

@@ -96,7 +96,15 @@ static ssize_t isl68137_avs_enable_show_page(struct i2c_client *client,
 					     int page,
 					     char *buf)
 {
-	int val = pmbus_read_byte_data(client, page, PMBUS_OPERATION);
+	int val;
+
+	val = pmbus_lock_interruptible(client);
+	if (val)
+		return val;
+
+	val = pmbus_read_byte_data(client, page, PMBUS_OPERATION);
+
+	pmbus_unlock(client);
 
 	if (val < 0)
 		return val;
@@ -118,6 +126,10 @@ static ssize_t isl68137_avs_enable_store_page(struct i2c_client *client,
 
 	op_val = result ? ISL68137_VOUT_AVS : 0;
 
+	rc = pmbus_lock_interruptible(client);
+	if (rc)
+		return rc;
+
 	/*
 	 * Writes to VOUT setpoint over AVSBus will persist after the VRM is
 	 * switched to PMBus control. Switching back to AVSBus control
@@ -129,17 +141,20 @@ static ssize_t isl68137_avs_enable_store_page(struct i2c_client *client,
 		rc = pmbus_read_word_data(client, page, 0xff,
 					  PMBUS_VOUT_COMMAND);
 		if (rc < 0)
-			return rc;
+			goto unlock;
 
 		rc = pmbus_write_word_data(client, page, PMBUS_VOUT_COMMAND,
 					   rc);
 		if (rc < 0)
-			return rc;
+			goto unlock;
 	}
 
 	rc = pmbus_update_byte_data(client, page, PMBUS_OPERATION,
 				    ISL68137_VOUT_AVS, op_val);
 
+unlock:
+	pmbus_unlock(client);
+
 	return (rc < 0) ? rc : count;
 }