[RFC PATCHv2 00/19] power_supply: Allow safe usage of power supply

[Krzysztof Kozlowski]

On śro, 2015-01-21 at 16:22 +0100, Sebastian Reichel wrote:
> Hi Krzysztof,
> 
> On Mon, Jan 05, 2015 at 04:47:43PM +0100, Krzysztof Kozlowski wrote:
> > This is RFC, please don't apply yet but let me know if this approach
> > is OK.
> 
> I just reviewed the patchset. It looks fine to me.

Great! Thanks for looking at patchset. I'll start working on next
version adjusting all drivers.

> 
> > TLDR
> > ====
> > Patchset tries to fix following race scenario:
> > 
> > Thread 1: charger manager, CONSUMER
> > Thread 2: power supply driver, PROVIDER
> > 
> > THREAD 1 (charger manager)         THREAD 2 (power supply driver)
> > ==========================         ==============================
> > psy = power_supply_get_by_name()
> >                                    Driver unbind, .remove
> >                                      power_supply_unregister()
> >                                      Device fully removed
> > psy->get_property()
> > 
> > To properly fix the race the patchset:
> > 1. Adds power_supply_get_property()-like API for safe access by consumer.
> > 2. Moves ownership of power_supply structure from driver (provider) to
> >    power supply core.
> > 3. Adds power_supply_put() which will reclaim memory.
> 
> Looks fine to me, thanks for doing this :)
> 
> > Description
> > =========== 
> > This is a little different than my previous approaches [1][2] for fixing
> > usage of power supply by some consumer, if driver implementing it is
> > unbound.
> > 
> > The patchset is quite big and touches power supply API so a lot of
> > changes in drivers are needed. These changes *are not finished yet*.
> > I've done them only for:
> >  - bq24190_charger.c
> >  - charger-manager.c
> >  - max14577_charger.c
> >  - max17040_battery.c
> >  - max17042_battery.c
> >  - sbs-battery.c
> >  - tps65090-charger.c
> > So allyesconfig won't build.
> >
> > If this approach is OK, I'll prepare full patchset changing all the
> > drivers.
> 
> Please do :)
> 
> > My previous approach [1][2] limited the race but did not close it.
> > Still the consumer of power supply by calling power_supply_get_propert(psy...)
> > may reference invalid memory because the producer freed it.
> > 
> > Actually, because struct power_supply is exposed to consumers, the
> > core should be the owner of it. This is accomplished in patch 11/19
> > ("power_supply: Change ownership from driver to core").
> > 
> > What the patchset does in steps
> > ===============================
> > 1. Some preparation steps are necessary - patch 1 and 2. The driver
> >    implementing power supply won't be able to fill structure before
> >    calling power_supply_register(). So 'power_supply_config'
> >    is introduced in patch 2 ("power_supply: Move run-time configuration
> >    to separate structure"). Unfortunately this touches all drivers.
> 
> $ grep -l power_supply_register **/*.c | grep -v mod.c | grep -v drivers/power
> drivers/acpi/ac.c
> drivers/acpi/battery.c
> drivers/acpi/sbs.c
> drivers/hid/hid-input.c
> drivers/hid/hid-sony.c
> drivers/hid/hid-wiimote-modules.c
> drivers/hid/wacom_sys.c
> drivers/platform/x86/compal-laptop.c
> drivers/staging/nvec/nvec_power.c
> 
> Please make sure to CC the respective maintainers for the patchset
> (e.g. current patch 14 and 15 should have CC'd x86 maintainers), so
> that they can Acknowledge the patchset.

Right. Probably maintainers should receive full patchset anyway. The
address list will be quite big.

> 
> > 2. Safe API wrappers (and usage counter) are added (power_supply_*()).
> > 3. Patch 11: ownership of 'struct power_supply' is moved from driver
> >    to the core.
> > 4. power_supply_put() is added which reclaims resources.
> 
> Looks fine to me.
> 
> > The patchset is rebased on next-20141226. It should be pulled at once.
> > Bisectability is preserved.
> 
> Fine with me, but I need acks from all involved maintainers. So for the
> patchset:
> 
> Reviewed-By: Sebastian Reichel <sre at kernel.org>

Thanks!

Best regards,
Krzysztof