linux-kernel - Re: [RFC PATCHv2 00/19] power_supply: Allow safe usage of power supply

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Date:	Wed, 21 Jan 2015 16:22:17 +0100
From:	Sebastian Reichel <sre@...nel.org>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <lenb@...nel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Pavel Machek <pavel@....cz>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-acpi@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [RFC PATCHv2 00/19] power_supply: Allow safe usage of power
 supply

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.

> 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.

> 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@...nel.org>

-- Sebastian

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