Re: [PATCH] hwmon: (gpio-fan) Fix runtime PM imbalance in probe and teardown

[sashiko-bot@kernel.org]

> In gpio_fan_probe(), gpio_fan_stop() is registered conditionally as a
> devres action before runtime PM is initialized, while gpio_fan_stop()
> unconditionally calls pm_runtime_disable(). This breaks runtime PM
> disable_depth and usage_count invariants across several paths:
> 
> - On alarm-only devices without control GPIOs, gpio_fan_stop() is never
>   registered, leaving pm_runtime_enable() unbalanced on unbind and
>   triggering "Unbalanced pm_runtime_enable!" on subsequent binds.
> - When control GPIOs are present and devm_add_action_or_reset(), hwmon
>   registration, or fan_alarm_init() fails, gpio_fan_stop() runs before
>   pm_runtime_enable(), incrementing disable_depth to 2 (leaving runtime
>   PM permanently disabled on re-probe) and, if speed_index > 0,
>   underflowing usage_count via pm_runtime_put_sync().
> - If pm_runtime_resume_and_get() fails when speed_index > 0, it drops
>   its reference while speed_index remains non-zero, causing
>   gpio_fan_stop() to call pm_runtime_put_sync() and underflow
>   usage_count.
> - Registering the hwmon device before enabling runtime PM exposes sysfs
>   attributes that can invoke set_fan_speed() before runtime PM state is
>   initialized.
> 
> Initialize runtime PM upfront with pm_runtime_set_suspended() and
> devm_pm_runtime_enable(), remove pm_runtime_disable() from
> gpio_fan_stop(), and acquire the initial active runtime PM reference
> before registering gpio_fan_stop() and the hwmon device.
> 
> Fixes: 0d01110e6356 ("hwmon: (gpio-fan) Add regulator support")
> Reported-by: Sashiko <sashiko@sashiko.dev>
> Link: https://sashiko.dev/#/bug/linux-349aa3ba-30c3-4c3c-b47e-f52839af2b8d
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Sashiko has reviewed this patch and found no issues.

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