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Message-ID: <4c12cab4-6265-78c0-46ce-d4014c9919fe@gmail.com>
Date:   Mon, 21 Feb 2022 15:59:06 +0300
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Subject: Re: [PATCH v3 2/4] hwmon: (lm90) Use hwmon_notify_event()
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To:     Jon Hunter <jonathanh@nvidia.com>,
        Jean Delvare <jdelvare@suse.com>,
        Guenter Roeck <linux@roeck-us.net>,
        Matt Merhar <mattmerhar@protonmail.com>
Cc:     linux-kernel@vger.kernel.org, linux-hwmon@vger.kernel.org,
        linux-tegra@vger.kernel.org
References: <20210618215455.19986-1-digetx@gmail.com>
 <20210618215455.19986-3-digetx@gmail.com>
 <9580f660-2a11-40e4-2986-f05703822d72@nvidia.com>
 <8d0c818a-d714-d8ab-f825-073cf549b959@gmail.com>
 <13b07bb3-90e4-a501-469c-ce64bc90bfd5@nvidia.com>
From:   Dmitry Osipenko <digetx@gmail.com>
In-Reply-To: <13b07bb3-90e4-a501-469c-ce64bc90bfd5@nvidia.com>
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21.02.2022 15:56, Jon Hunter пишет:
> 
> 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.

The interrupt is threaded, so it can take a mutex.