Messages in this thread | | | Date | Wed, 22 Jun 2016 16:37:17 +0200 | From | Sebastian Reichel <> | Subject | Re: [PATCH v2] power_supply: fix return value of get_property |
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Hi,
On Tue, Jun 21, 2016 at 02:08:05PM -0400, Rhyland Klein wrote: > On 6/16/2016 11:40 AM, Rhyland Klein wrote: > > On 6/16/2016 4:43 AM, Krzysztof Kozlowski wrote: > >> On 06/16/2016 12:13 AM, Rhyland Klein wrote: > >>> power_supply_get_property() should ideally return -EAGAIN if it is > >>> called while the power_supply is being registered. There was no way > >>> previously to determine if use_cnt == 0 meant that the power_supply > >>> wasn't fully registered yet, or if it had already been unregistered. > >>> > >>> Add a new boolean to the power_supply struct to simply show if > >>> registration is completed. Lastly, modify the check in > >>> power_supply_show_property() to also ignore -EAGAIN when so it > >>> doesn't complain about not returning the property. > >>> > >>> Signed-off-by: Rhyland Klein <rklein@nvidia.com> > >>> --- > >>> v2: > >>> - Modify power_supply_show_property() to not complain if it > >>> sees a return value of -EAGAIN after calling > >>> power_supply_get_property(). > >>> > >>> drivers/power/power_supply_core.c | 6 +++++- > >>> drivers/power/power_supply_sysfs.c | 2 +- > >>> include/linux/power_supply.h | 1 + > >>> 3 files changed, 7 insertions(+), 2 deletions(-) > >> > >> I don't like it for two reasons: > >> 1. There is still a short window when the information will be > >> inaccurate. See comment below. > >> > >> 2. Although the code is not very complicated but it adds another field > >> and some checks just for differentiating EAGAIN/ENODEV. It is > >> unnecessary complexity. > >> > >>> > >>> diff --git a/drivers/power/power_supply_core.c b/drivers/power/power_supply_core.c > >>> index b13cd074c52a..a39a47672979 100644 > >>> --- a/drivers/power/power_supply_core.c > >>> +++ b/drivers/power/power_supply_core.c > >>> @@ -491,8 +491,11 @@ int power_supply_get_property(struct power_supply *psy, > >>> enum power_supply_property psp, > >>> union power_supply_propval *val) > >>> { > >>> - if (atomic_read(&psy->use_cnt) <= 0) > >>> + if (atomic_read(&psy->use_cnt) <= 0) { > >>> + if (!psy->initialized) > >>> + return -EAGAIN; > >>> return -ENODEV; > >>> + } > >>> > >>> return psy->desc->get_property(psy, psp, val); > >>> } > >>> @@ -775,6 +778,7 @@ __power_supply_register(struct device *parent, > >>> if (rc) > >>> goto create_triggers_failed; > >>> > >>> + psy->initialized = true; > >> > >> If someone calls power_supply_get_property() here, then ENODEV will be > >> returned which is wrong. > >> > >> The problem is not solved entirely... I am not convinced that introduced > >> complexity is worth fixing it. > >> > > > > Right now, without this patch, this causes the thermal function > > "update_temperature" in: > > > > thermal_zone_device_register-> > > thermal_zone_device_update-> > > update_temperature > > (->thermal_zone_get_temp() from the original stack) > > > > to print a warning as it sees ret != -EAGAIN. This causes a warning > > "failed to read out thermal zone". I think the idea there is if anything > > other than "try again" it complains. While this doesn't cause functional > > problems, I do think avoid the warning is worth while. > > > > I think that there is an onus on the power_supply code to be accurate in > > its return codes, and EAGAIN is the correct one we should be returning. > > I don't see how someone would call power_supply_get_property, but I > > agree there is the possibility that if someone did call there, that it > > could return the wrong value. > > > > We could wrap the setting of initialized and use_cnt inside a mutex, > > which should prevent anyone calling anything in between if we wanted to > > completely plug that hole. I am not fond of the idea of adding a struct > > member for such a small, specific case, but as we found before, I don't > > think there is another way to differentiate otherwise. > > > > Sebastian, do you have an opinion on this?
Instead of adding a mutex, just set "psy->initialized = true" after increment of use_cnt. I'm fine with the patch otherwise.
-- Sebastian [unhandled content-type:application/pgp-signature] | |