Re: [PATCH v3 2/4] hwmon: (lm90) Use hwmon_notify_event()

Jon Hunter
2022-02-21T15:49:33Z

On 21/02/2022 15:43, Guenter Roeck wrote:

...

>> We observed a random null pointer deference crash somewhere in the
>> thermal core (crash log below is not very helpful) when calling
>> mutex_lock(). It looks like we get an interrupt when this crash
>> happens.
>>
>> Looking at the lm90 driver, per the above, I now see we are calling
>> hwmon_notify_event() from the lm90 interrupt handler. Looking at
>> hwmon_notify_event() I see that ...
>>
>> hwmon_notify_event()
>>    --> hwmon_thermal_notify()
>>      --> thermal_zone_device_update()
>>        --> update_temperature()
>>          --> mutex_lock()
>>
>> So although I don't completely understand the crash, it does seem
>> that we should not be calling hwmon_notify_event() from the
>> interrupt handler.
>>
> As mentioned separately, this is not the problem.

Yes I can see that now.

> I think the problem may be that this is not a devicetree system
> (or the lm90 devide does not have a devicetree node), but thermal
> notification currently only works in such systems because the hwmon
> subsystem uses the devicetree registration method. At the same time,
> CONFIG_THERMAL_OF is obviously enabled. Unfortunately, the hwmon code
> does not bail out in that situation due to another bug.

The platform I see this on does use device-tree and it does have a node
for the ti,tmp451 device which uses the lm90 device. This platform uses
the device-tree source
arch/arm64/boot/dts/nvidia/tegra194-p2972-0000.dts and the tmp451 node
is in arch/arm64/boot/dts/nvidia/tegra194-p2888.dtsi.

Cheers
Jon

--
nvpublic