Re: [PATCH 1/5] ACPI: battery: Do not unload battery hooks on single error

[Armin Wolf]

Am 19.09.22 um 21:12 schrieb Armin Wolf:

> Am 19.09.22 um 18:27 schrieb Rafael J. Wysocki:
>
> > On Mon, Sep 19, 2022 at 12:42 PM Hans de Goede <hdegoede@xxxxxxxxxx> 
> > wrote:
> > > Hi,
> > >
> > > On 9/12/22 13:53, Armin Wolf wrote:
> > > > Currently, battery hooks are being unloaded if they return
> > > > an error when adding a single battery.
> > > > This however also causes the removal of successfully added
> > > > hooks if they return -ENODEV for a single unsupported
> > > > battery.
> > > >
> > > > Do not unload battery hooks in such cases since the hook
> > > > handles any cleanup actions.
> > > >
> > > > Signed-off-by: Armin Wolf <W_Armin@xxxxxx>
> > > Maybe instead of removing all error checking, allow -ENODEV
> > > and behave as before when the error is not -ENODEV ?
> > >
> > > Otherwise we should probably make the add / remove callbacks
> > > void to indicate that any errors are ignored.
> > >
> > > Rafael, do you have any opinion on this?
> > IMV this is not a completely safe change, because things may simply
> > not work in the cases in which an error is returned.
> >
> > It would be somewhat better to use a special error code to indicate
> > "no support" (eg. -ENOTSUPP) and ignore that one only.
>
> I would favor -ENODEV then, since it is already used by quiet a few 
> drivers
> to indicate a unsupported battery.
>
> Armin Wolf
While checking all instances where the battery hook mechanism is currently used,
i found out that all but a single battery hook return -ENODEV for all errors they
encounter, the exception being the huawei-wmi driver.

I do not know the reason for this, but i fear unloading the extension on for
example -ENOTSUP will result in similar behavior by hooks wanting to avoid being
unloaded on harmless errors.

However, i agree that when ignoring all errors, battery extensions which provide
similar attributes may currently delete each others attributes.

Any idea on how to solve this?

Armin Wolf

> > > > ---
> > > >   drivers/acpi/battery.c | 24 +++---------------------
> > > >   1 file changed, 3 insertions(+), 21 deletions(-)
> > > >
> > > > diff --git a/drivers/acpi/battery.c b/drivers/acpi/battery.c
> > > > index 306513fec1e1..e59c261c7c59 100644
> > > > --- a/drivers/acpi/battery.c
> > > > +++ b/drivers/acpi/battery.c
> > > > @@ -724,20 +724,10 @@ void battery_hook_register(struct 
> > > > acpi_battery_hook *hook)
> > > >         * its attributes.
> > > >         */
> > > >        list_for_each_entry(battery, &acpi_battery_list, list) {
> > > > -             if (hook->add_battery(battery->bat)) {
> > > > -                     /*
> > > > -                      * If a add-battery returns non-zero,
> > > > -                      * the registration of the extension has failed,
> > > > -                      * and we will not add it to the list of loaded
> > > > -                      * hooks.
> > > > -                      */
> > > > -                     pr_err("extension failed to load: %s", 
> > > > hook->name);
> > > > -                     __battery_hook_unregister(hook, 0);
> > > > -                     goto end;
> > > > -             }
> > > > +             hook->add_battery(battery->bat);
> > > >        }
> > > >        pr_info("new extension: %s\n", hook->name);
> > > > -end:
> > > > +
> > > >        mutex_unlock(&hook_mutex);
> > > >   }
> > > >   EXPORT_SYMBOL_GPL(battery_hook_register);
> > > > @@ -762,15 +752,7 @@ static void battery_hook_add_battery(struct 
> > > > acpi_battery *battery)
> > > >         * during the battery module initialization.
> > > >         */
> > > >        list_for_each_entry_safe(hook_node, tmp, &battery_hook_list, 
> > > > list) {
> > > > -             if (hook_node->add_battery(battery->bat)) {
> > > > -                     /*
> > > > -                      * The notification of the extensions has 
> > > > failed, to
> > > > -                      * prevent further errors we will unload the 
> > > > extension.
> > > > -                      */
> > > > -                     pr_err("error in extension, unloading: %s",
> > > > -                                     hook_node->name);
> > > > -                     __battery_hook_unregister(hook_node, 0);
> > > > -             }
> > > > +             hook_node->add_battery(battery->bat);
> > > >        }
> > > >        mutex_unlock(&hook_mutex);
> > > >   }
> > > > --
> > > > 2.30.2