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

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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


--
nvpublic



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