[PATCH] hwmon: Handle failure to register sensor with thermal zone correctly

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

If an attempt is made to a sensor with a thermal zone and it fails,
the call to devm_thermal_zone_of_sensor_register() may return -ENODEV.
This may result in crashes similar to the following.

Unable to handle kernel NULL pointer dereference at virtual address 00000000000003cd
...
Internal error: Oops: 96000021 [#1] PREEMPT SMP
...
pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : mutex_lock+0x18/0x60
lr : thermal_zone_device_update+0x40/0x2e0
sp : ffff800014c4fc60
x29: ffff800014c4fc60 x28: ffff365ee3f6e000 x27: ffffdde218426790
x26: ffff365ee3f6e000 x25: 0000000000000000 x24: ffff365ee3f6e000
x23: ffffdde218426870 x22: ffff365ee3f6e000 x21: 00000000000003cd
x20: ffff365ee8bf3308 x19: ffffffffffffffed x18: 0000000000000000
x17: ffffdde21842689c x16: ffffdde1cb7a0b7c x15: 0000000000000040
x14: ffffdde21a4889a0 x13: 0000000000000228 x12: 0000000000000000
x11: 0000000000000000 x10: 0000000000000000 x9 : 0000000000000000
x8 : 0000000001120000 x7 : 0000000000000001 x6 : 0000000000000000
x5 : 0068000878e20f07 x4 : 0000000000000000 x3 : 00000000000003cd
x2 : ffff365ee3f6e000 x1 : 0000000000000000 x0 : 00000000000003cd
Call trace:
 mutex_lock+0x18/0x60
 hwmon_notify_event+0xfc/0x110
 0xffffdde1cb7a0a90
 0xffffdde1cb7a0b7c
 irq_thread_fn+0x2c/0xa0
 irq_thread+0x134/0x240
 kthread+0x178/0x190
 ret_from_fork+0x10/0x20
Code: d503201f d503201f d2800001 aa0103e4 (c8e47c02)

Jon Hunter reports that the exact call sequence is:

hwmon_notify_event()
  --> hwmon_thermal_notify()
    --> thermal_zone_device_update()
      --> update_temperature()
        --> mutex_lock()

The hwmon core needs to handle all errors returned from calls
to devm_thermal_zone_of_sensor_register(). If the call fails
with -ENODEV, report the problem as warning but continue to
register the hwmon device.

Reported-by: Jon Hunter <jonathanh@nvidia.com>
Cc: Dmitry Osipenko <digetx@gmail.com>
Fixes: 1597b374af222 ("hwmon: Add notification support")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 drivers/hwmon/hwmon.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/hwmon/hwmon.c b/drivers/hwmon/hwmon.c
index 3501a3ead4ba..4bfe3791a5ba 100644
--- a/drivers/hwmon/hwmon.c
+++ b/drivers/hwmon/hwmon.c
@@ -214,12 +214,14 @@ static int hwmon_thermal_add_sensor(struct device *dev, int index)
 
 	tzd = devm_thermal_zone_of_sensor_register(dev, index, tdata,
 						   &hwmon_thermal_ops);
-	/*
-	 * If CONFIG_THERMAL_OF is disabled, this returns -ENODEV,
-	 * so ignore that error but forward any other error.
-	 */
-	if (IS_ERR(tzd) && (PTR_ERR(tzd) != -ENODEV))
-		return PTR_ERR(tzd);
+	if (IS_ERR(tzd)) {
+		if (PTR_ERR(tzd) != -ENODEV)
+			return PTR_ERR(tzd);
+		dev_warn(dev, "Failed to register temp%d_input with thermal zone\n",
+			 index + 1);
+		devm_kfree(dev, tdata);
+		return 0;
+	}
 
 	err = devm_add_action(dev, hwmon_thermal_remove_sensor, &tdata->node);
 	if (err)
-- 
2.35.1