On Tuesday 26 May 2020 21:16:28 Andrew F. Davis wrote:
> On 5/25/20 7:32 AM, Krzysztof Kozlowski wrote:
> > This reverts commit 8cfaaa811894a3ae2d7360a15a6cfccff3ebc7db.
> >
> > If device was unbound and bound, the polling interval would be set to 0.
> > This is both unexpected and messes up with other bq27xxx devices (if
> > more than one battery device is used).
> >
> > This reset of polling interval was added in commit 8cfaaa811894
> > ("bq27x00_battery: Fix OOPS caused by unregistring bq27x00 driver")
> > stating that power_supply_unregister() calls get_property(). However in
> > Linux kernel v3.1 and newer, such call trace does not exist.
> > Unregistering power supply does not call get_property() on unregistered
> > power supply.
> >
> > Fixes: 8cfaaa811894 ("bq27x00_battery: Fix OOPS caused by unregistring bq27x00 driver")
> > Cc: <stable@xxxxxxxxxxxxxxx>
> > Signed-off-by: Krzysztof Kozlowski <krzk@xxxxxxxxxx>
> >
> > ---
> >
> > I really could not identify the issue being fixed in offending commit
> > 8cfaaa811894 ("bq27x00_battery: Fix OOPS caused by unregistring bq27x00
> > driver"), therefore maybe I missed here something important.
> >
> > Please share your thoughts on this.
>
>
> I'm having a hard time finding the OOPS also. Maybe there is a window
> where the poll function is running or about to run where
> cancel_delayed_work_sync() is called and cancels the work, only to have
> an interrupt or late get_property call in to the poll function and
> re-schedule it.
>
> What we really need is to do is look at how we are handling the polling
> function. It gets called from the workqueue, from a threaded interrupt
> context, and from a power supply framework callback, possibly all at the
> same time. Sometimes its protected by a lock, sometimes not. Updating
> the device's cached data should always be locked.
>
> What's more is the poll function is self-arming, so if we call
> cancel_delayed_work_sync() (remove it from the work queue then then wait
> for it to finish if running), are we sure it wont have just re-arm itself?
>
> We should make the only way we call the poll function be through the
> work queue, (plus make sure all accesses to the cache are locked).
>
> Andrew
I do not remember details too. It is long time ago.
CCing Ivaylo Dimitrov as he may remember something...
>
> > ---
> > drivers/power/supply/bq27xxx_battery.c | 8 --------
> > 1 file changed, 8 deletions(-)
> >
> > diff --git a/drivers/power/supply/bq27xxx_battery.c b/drivers/power/supply/bq27xxx_battery.c
> > index 942c92127b6d..4c94ee72de95 100644
> > --- a/drivers/power/supply/bq27xxx_battery.c
> > +++ b/drivers/power/supply/bq27xxx_battery.c
> > @@ -1905,14 +1905,6 @@ EXPORT_SYMBOL_GPL(bq27xxx_battery_setup);
> >
> > void bq27xxx_battery_teardown(struct bq27xxx_device_info *di)
> > {
> > - /*
> > - * power_supply_unregister call bq27xxx_battery_get_property which
> > - * call bq27xxx_battery_poll.
> > - * Make sure that bq27xxx_battery_poll will not call
> > - * schedule_delayed_work again after unregister (which cause OOPS).
> > - */
> > - poll_interval = 0;
> > -
> > cancel_delayed_work_sync(&di->work);
> >
> > power_supply_unregister(di->bat);
> >
