Re: [PATCH] Fix sysfs_notify and kobject_uevent in fan_alarm_notify

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Ok, seems that moving that block, where fan_alarm_init is called down, isn't a problem on master. I need to use 4.9, cause we have an embedded device that needs patches, and they are only available for older kernels.

In 4.9, fan_alarm_init() does fan_data->alarm = alarm;
When fan_alarm_init() is called after devm_hwmon_device_register_with_groups(), then fan_data->alarm is not yet set, so the sysfs attribute is not created.

when I move the fan_data->alarm = alarm; out of fan_alarm_init() before devm_hwmon_device_register_with_groups() and the fan_alarm_init() after, then it works, and doesn't have a race condition.

On master, populating fan_data->alarm_gpio is done in gpio_fan_get_of_data(fan_data); as far as I understand, so moving the fan_alarm_init() block further down shouldn't be a problem.

I don't know, how I can test this with master kernel. Unfortunately, the device, I'm using doesn't have a recent kernel. And on my normal (desktop) pc, I don't have a gpio fan.
How should I proceed now?


BR, Christian

Am 19.06.2019 um 09:47 schrieb Christian Schneider:
Hi,
unfrotunately I found a problem with my patch. It didn't appear on the devices, where I tested, only when distributing the patch to more devices, it occurs sometimes.

There is a possible race condition. In gpio_fan_probe, the IRQ handler for the fan alarm is registered before the hwmon_dev is initialised. So it is possible, that the handler executes, while fandata->hwmon_dev is still unitialised and the handler runs in an invalid pointer dereference.

The obvious fix, moving the
/* Configure alarm GPIO if available. */
if (fan_data->alarm_gpio) {
     err = fan_alarm_init(fan_data);
     if (err)
         return err;
}
block after

/* Make this driver part of hwmon class. */
fan_data->hwmon_dev =
     devm_hwmon_device_register_with_groups(dev,
                            "gpio_fan", fan_data,
                            gpio_fan_groups);

doesn't work. Sysfs doesn't have a fan1_alarm attribute anymore then.

It is not yet clear to me, why creation of the attribute fails in this case. I need to investigate further.
In the meanwhile, please revert my patch.

I'm sorry for the disturbance I created....

BR, Christian


Am 17.06.2019 um 18:04 schrieb Guenter Roeck:
On Mon, Jun 17, 2019 at 11:33:43AM +0200, cschneider@xxxxxxxxxxxxx wrote:
From: Christian Schneider <christian@xxxxxxxx>

sysfs_notify and kobject_uevent are passed the wrong kobject.
that why notifications can't be received and uevents have the wrong path.
this patch fixes this.

Signed-off-by: Christian Schneider <cschneider@xxxxxxxxxxxxx>

Applied.

In the future, please version your patches, add a change log,
and reflect the subsystem and driver in the subject line.

Thanks,
Guenter

---
  drivers/hwmon/gpio-fan.c | 4 ++--
  1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/hwmon/gpio-fan.c b/drivers/hwmon/gpio-fan.c
index 84753680a4e8..76377791ff0e 100644
--- a/drivers/hwmon/gpio-fan.c
+++ b/drivers/hwmon/gpio-fan.c
@@ -54,8 +54,8 @@ static void fan_alarm_notify(struct work_struct *ws)
      struct gpio_fan_data *fan_data =
          container_of(ws, struct gpio_fan_data, alarm_work);
-    sysfs_notify(&fan_data->dev->kobj, NULL, "fan1_alarm");
-    kobject_uevent(&fan_data->dev->kobj, KOBJ_CHANGE);
+    sysfs_notify(&fan_data->hwmon_dev->kobj, NULL, "fan1_alarm");
+    kobject_uevent(&fan_data->hwmon_dev->kobj, KOBJ_CHANGE);
  }
  static irqreturn_t fan_alarm_irq_handler(int irq, void *dev_id)



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