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

[Jon Hunter <jonathanh@xxxxxxxxxx>]

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@xxxxxxxxxxxx>
> > > Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx>
> > > ---
> > >    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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