Re: [PATCH] platform/x86: dell-laptop: Fix crash when unregistering battery hook

[Armin Wolf]

Am 19.09.24 um 09:13 schrieb Andres Salomon:

> On Thu, 19 Sep 2024 08:33:32 +0200
> Armin Wolf <W_Armin@xxxxxx> wrote:
>
> > If the battery hook encounters a unsupported battery, it will
> > return an error. This in turn will cause the battery driver to
> > automatically unregister the battery hook.
> >
> > However as soon as the driver itself attempts to unregister the
> > already unregistered battery hook, a crash occurs due to a
> > corrupted linked list.
> >
> > Fix this by simply ignoring unsupported batteries.
> >
> > Tested on a Dell Inspiron 3505.
> >
> > Fixes: ab58016c68cc ("platform/x86:dell-laptop: Add knobs to change battery charge settings")
> > Signed-off-by: Armin Wolf <W_Armin@xxxxxx>
> > ---
> > I CCed the maintainers of the ACPI battery driver since i believe
> > that this patch highlights a general issue inside the battery hook
> > mechanism.
> >
> > This is because the same crash will be triggered should for example
> > device_add_groups() fail.
> >
> > Any ideas on how to solve this problem?
> > ---
> Hm, I see that when battery_hook_register() has the add_battery hook fail,
> then __battery_hook_unregister() calls the remove_battery hook. Does
> something like the following fix it?
>
> (note: not any kind of final patch, just a test.)

Not really, since the error can happen even while a new battery is being added,
which can happen anytime (even during battery hook removal). This means that using
a global variable would be prone to race conditions.

The issue can only be solved inside the ACPI battery driver itself, that is the reason
why i CCed the ACPI maintainers.

Aside from that, ignoring unsupported batteries allows the driver to work on
machines with multiple batteries.

Thanks,
Armin Wolf

> ---
>   drivers/platform/x86/dell/dell-laptop.c | 12 ++++++++++--
>   1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/platform/x86/dell/dell-laptop.c b/drivers/platform/x86/dell/dell-laptop.c
> index a9de19799f01..c7b92b2f7ed2 100644
> --- a/drivers/platform/x86/dell/dell-laptop.c
> +++ b/drivers/platform/x86/dell/dell-laptop.c
> @@ -2390,21 +2390,29 @@ static struct attribute *dell_battery_attrs[] = {
>   	NULL,
>   };
>   ATTRIBUTE_GROUPS(dell_battery);
> +static bool bgroup_registered = false;
>
>   static int dell_battery_add(struct power_supply *battery,
>   		struct acpi_battery_hook *hook)
>   {
> +	int err;
> +
>   	/* this currently only supports the primary battery */
>   	if (strcmp(battery->desc->name, "BAT0") != 0)
>   		return -ENODEV;
>
> -	return device_add_groups(&battery->dev, dell_battery_groups);
> +	err = device_add_groups(&battery->dev, dell_battery_groups);
> +	if (!err)
> +		bgroup_registered = true;
> +
> +	return err;
>   }
>
>   static int dell_battery_remove(struct power_supply *battery,
>   		struct acpi_battery_hook *hook)
>   {
> -	device_remove_groups(&battery->dev, dell_battery_groups);
> +	if (bgroup_registered)
> +		device_remove_groups(&battery->dev, dell_battery_groups);
>   	return 0;
>   }