linux-kernel - Re: [PATCH v3 2/4] hwmon: (lm90) Use hwmon_notify

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Date:   Mon, 21 Feb 2022 15:49:16 +0000
From:   Jon Hunter <jonathanh@...dia.com>
To:     Guenter Roeck <linux@...ck-us.net>,
        Dmitry Osipenko <digetx@...il.com>,
        Jean Delvare <jdelvare@...e.com>
Cc:     linux-kernel@...r.kernel.org, linux-hwmon@...r.kernel.org,
        linux-tegra@...r.kernel.org
Subject: Re: [PATCH v3 2/4] hwmon: (lm90) Use hwmon_notify_event()


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