Re: [PATCH] platform/x86: dell-ddv: Fix taking the psy->extensions_sem lock twice

[Armin Wolf <W_Armin@gmx.de>]

Am 20.06.25 um 19:58 schrieb Hans de Goede:

> dell_wmi_ddv_get_property() gets called with psy->extensions_sem
> read-locked, it calls dell_wmi_ddv_battery_translate() which calls
> power_supply_get_property() on the same psy which again read-locks
> psy->extensions_sem.
>
> Lockdep rightfully complains about this:
>
>   ============================================
>   WARNING: possible recursive locking detected
> ...
>   kworker/16:3/1230 is trying to acquire lock:
>   ffff8c3143417658 (&psy->extensions_sem){++++}-{4:4},
>    at: power_supply_get_property.part.0+0x23/0x160
>   but task is already holding lock:
>   ffff8c3143417658 (&psy->extensions_sem){++++}-{4:4},
>    at: power_supply_get_property.part.0+0x23/0x160
> ...
>    Possible unsafe locking scenario:
>
>          CPU0
>          ----
>     lock(&psy->extensions_sem);
>     lock(&psy->extensions_sem);
>
>    *** DEADLOCK ***
> ...
>   Call Trace:
>    <TASK>
>    ...
>    down_read+0x3e/0x180
>    ? power_supply_get_property.part.0+0x23/0x160
>    power_supply_get_property.part.0+0x23/0x160
>    dell_wmi_ddv_battery_translate+0x68/0x1d0 [dell_wmi_ddv]
>    ? lock_acquire+0xd9/0x2c0
>    dell_wmi_ddv_get_property+0x25/0x240 [dell_wmi_ddv]
>    power_supply_get_property.part.0+0x87/0x160
>    power_supply_format_property+0xc4/0x3d0
>    add_prop_uevent+0x26/0x90
>    power_supply_uevent+0xb9/0xf0
>
> This usually works fine, because read-locking can be done multiple times
> but if someone tries to write-lock between the 2 read-lock calls then
> the second read-lock will block on the write-lock and the write-lock will
> be blocked on the first read-lock leading to a deadlock.
>
> The serial is part of the main psy device, not of an extension. Directly
> call psy->desc->get_property() in dell_wmi_ddv_battery_translate() to fix
> the double-lock issue.
>
> Note this also influences eppid_show() which is called directly rather
> then through power_supply_get_property(). This is ok since the ACPI
> battery is fully ready to be used when the battery hook's add_battery
> callback is called.

Thank you very much for finding this issue, but i think that simply calling battery->desc->get_property()
is not the right solution for this:

1. We should still call psy_desc_has_property() to determine if the power supply actually support
    POWER_SUPPLY_PROP_SERIAL_NUMBER.

2. At least another power supply extension user (the uniwill-laptop driver currently being under review)
    suffers from a similar problem, so a more generic solution is needed.

Maybe we could introduce a new function for reading power supply properties that ignores any
power supply extensions? This way future extension could use this function too.

I envision something like this:
	
int power_supply_get_property_direct(struct power_supply *psy,
			    enum power_supply_property psp,
			    union power_supply_propval *val)
{
	if (atomic_read(&psy->use_cnt) <= 0) {
		if (!psy->initialized)
			return -EAGAIN;
		return -ENODEV;
	}

	if (psy_desc_has_property(psy->desc, psp))
		return psy->desc->get_property(psy, psp, val);
	else if (power_supply_battery_info_has_prop(psy->battery_info, psp))
		return power_supply_battery_info_get_prop(psy->battery_info, psp, val);
	else
		return -EINVAL;
}
EXPORT_SYMBOL_GPL(power_supply_get_property_direct);

It basically is power_supply_get_property() without the extension logic. I can also write some
documentation on how to implement power supply extensions in general.

What do you thing?

Thanks,
Armin Wolf

> Fixes: 058de163a376 ("platform/x86: dell-ddv: Implement the battery matching algorithm")
> Signed-off-by: Hans de Goede <hansg@kernel.org>
> ---
>   drivers/platform/x86/dell/dell-wmi-ddv.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/platform/x86/dell/dell-wmi-ddv.c b/drivers/platform/x86/dell/dell-wmi-ddv.c
> index 67f3d7158403..95cc3139f271 100644
> --- a/drivers/platform/x86/dell/dell-wmi-ddv.c
> +++ b/drivers/platform/x86/dell/dell-wmi-ddv.c
> @@ -689,9 +689,11 @@ static int dell_wmi_ddv_battery_translate(struct dell_wmi_ddv_data *data,
>   
>   	dev_dbg(&data->wdev->dev, "Translation cache miss\n");
>   
> -	/* Perform a translation between a ACPI battery and a battery index */
> -
> -	ret = power_supply_get_property(battery, POWER_SUPPLY_PROP_SERIAL_NUMBER, &val);
> +	/*
> +	 * Perform a translation between a ACPI battery and a battery index. Directly call
> +	 * desc->get_property() to avoid locking battery->extensions_sem a second time.
> +	 */
> +	ret = battery->desc->get_property(battery, POWER_SUPPLY_PROP_SERIAL_NUMBER, &val);
>   	if (ret < 0)
>   		return ret;
>