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

Jon Hunter
2022-02-21T12:56:15Z

On 21/02/2022 12:36, Dmitry Osipenko wrote:
> 21.02.2022 15:01, Jon Hunter пишет:
>> Hi Dmitry,
>>
>> On 18/06/2021 22:54, Dmitry Osipenko wrote:
>>> Use hwmon_notify_event() to notify userspace and thermal core about
>>> temperature changes.
>>>
>>> Suggested-by: Guenter Roeck <linux@roeck-us.net>
>>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
>>> ---
>>>   drivers/hwmon/lm90.c | 44 +++++++++++++++++++++++++++++++++-----------
>>>   1 file changed, 33 insertions(+), 11 deletions(-)
>>>
>>> diff --git a/drivers/hwmon/lm90.c b/drivers/hwmon/lm90.c
>>> index 2e057fad05b4..e7b678a40b39 100644
>>> --- a/drivers/hwmon/lm90.c
>>> +++ b/drivers/hwmon/lm90.c
>>> @@ -465,6 +465,7 @@ enum lm90_temp11_reg_index {
>>>     struct lm90_data {
>>>       struct i2c_client *client;
>>> +    struct device *hwmon_dev;
>>>       u32 channel_config[4];
>>>       struct hwmon_channel_info temp_info;
>>>       const struct hwmon_channel_info *info[3];
>>> @@ -1731,22 +1732,41 @@ static bool lm90_is_tripped(struct i2c_client
>>> *client, u16 *status)
>>>         if ((st & (LM90_STATUS_LLOW | LM90_STATUS_LHIGH |
>>> LM90_STATUS_LTHRM)) ||
>>>           (st2 & MAX6696_STATUS2_LOT2))
>>> -        dev_warn(&client->dev,
>>> -             "temp%d out of range, please check!\n", 1);
>>> +        dev_dbg(&client->dev,
>>> +            "temp%d out of range, please check!\n", 1);
>>>       if ((st & (LM90_STATUS_RLOW | LM90_STATUS_RHIGH |
>>> LM90_STATUS_RTHRM)) ||
>>>           (st2 & MAX6696_STATUS2_ROT2))
>>> -        dev_warn(&client->dev,
>>> -             "temp%d out of range, please check!\n", 2);
>>> +        dev_dbg(&client->dev,
>>> +            "temp%d out of range, please check!\n", 2);
>>>       if (st & LM90_STATUS_ROPEN)
>>> -        dev_warn(&client->dev,
>>> -             "temp%d diode open, please check!\n", 2);
>>> +        dev_dbg(&client->dev,
>>> +            "temp%d diode open, please check!\n", 2);
>>>       if (st2 & (MAX6696_STATUS2_R2LOW | MAX6696_STATUS2_R2HIGH |
>>>              MAX6696_STATUS2_R2THRM | MAX6696_STATUS2_R2OT2))
>>> -        dev_warn(&client->dev,
>>> -             "temp%d out of range, please check!\n", 3);
>>> +        dev_dbg(&client->dev,
>>> +            "temp%d out of range, please check!\n", 3);
>>>       if (st2 & MAX6696_STATUS2_R2OPEN)
>>> -        dev_warn(&client->dev,
>>> -             "temp%d diode open, please check!\n", 3);
>>> +        dev_dbg(&client->dev,
>>> +            "temp%d diode open, please check!\n", 3);
>>> +
>>> +    if (st & LM90_STATUS_LLOW)
>>> +        hwmon_notify_event(data->hwmon_dev, hwmon_temp,
>>> +                   hwmon_temp_min, 0);
>>> +    if (st & LM90_STATUS_RLOW)
>>> +        hwmon_notify_event(data->hwmon_dev, hwmon_temp,
>>> +                   hwmon_temp_min, 1);
>>> +    if (st2 & MAX6696_STATUS2_R2LOW)
>>> +        hwmon_notify_event(data->hwmon_dev, hwmon_temp,
>>> +                   hwmon_temp_min, 2);
>>> +    if (st & LM90_STATUS_LHIGH)
>>> +        hwmon_notify_event(data->hwmon_dev, hwmon_temp,
>>> +                   hwmon_temp_max, 0);
>>> +    if (st & LM90_STATUS_RHIGH)
>>> +        hwmon_notify_event(data->hwmon_dev, hwmon_temp,
>>> +                   hwmon_temp_max, 1);
>>> +    if (st2 & MAX6696_STATUS2_R2HIGH)
>>> +        hwmon_notify_event(data->hwmon_dev, hwmon_temp,
>>> +                   hwmon_temp_max, 2);
>>
>>
>> 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.
>>
>> BTW I have not reproduced this myself yet, so I have just been
>> reviewing the code to try and understand this.
>
> Matt Merhar was experiencing a similar issue on T30 Ouya, but I never
> managed to reproduce it on Nexus 7 and Acer A500 tablets, and couldn't
> spot any problem in the code. IIRC, it was a NULL dereference of another
> pointer within that code.

OK. From looking at the above I don't think we can call
hwmon_notify_event() from an interrupt handler because this is going to
try and request a mutex. So we need to fix that.

Jon

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