Re: [PATCH v3] power_supply: power_supply_read_temp only if use_cnt > 0

[Krzysztof Kozlowski]

On 06/07/2016 10:26 PM, Rhyland Klein wrote:
> Change power_supply_read_temp() to use power_supply_get_property()
> so that it will check the use_cnt and ensure it is > 0. The use_cnt
> will be incremented at the end of __power_supply_register, so this
> will block to case where get_property can be called before the supply
> is fully registered. This fixes the issue show in the stack below:
> 
> [    1.452598] power_supply_read_temp+0x78/0x80
> [    1.458680] thermal_zone_get_temp+0x5c/0x11c
> [    1.464765] thermal_zone_device_update+0x34/0xb4
> [    1.471195] thermal_zone_device_register+0x87c/0x8cc
> [    1.477974] __power_supply_register+0x364/0x424
> [    1.484317] power_supply_register_no_ws+0x10/0x18
> [    1.490833] bq27xxx_battery_setup+0x10c/0x164
> [    1.497003] bq27xxx_battery_i2c_probe+0xd0/0x1b0
> [    1.503435] i2c_device_probe+0x174/0x240
> [    1.509172] driver_probe_device+0x1fc/0x29c
> [    1.515167] __driver_attach+0xa4/0xa8
> [    1.520643] bus_for_each_dev+0x58/0x98
> [    1.526204] driver_attach+0x20/0x28
> [    1.531505] bus_add_driver+0x1c8/0x22c
> [    1.537067] driver_register+0x68/0x108
> [    1.542630] i2c_register_driver+0x38/0x7c
> [    1.548457] bq27xxx_battery_i2c_driver_init+0x18/0x20
> [    1.555321] do_one_initcall+0x38/0x12c
> [    1.560886] kernel_init_freeable+0x148/0x1ec
> [    1.566972] kernel_init+0x10/0xfc
> [    1.572101] ret_from_fork+0x10/0x40
> 
> Also make the same change to ps_get_max_charge_cntl_limit() and
> ps_get_cur_chrage_cntl_limit() to be safe. Lastly, change the return
> value of power_supply_get_property() to -EAGAIN from -ENODEV if
> use_cnt <= 0.
> 
> Fixes: 297d716f6260 ("power_supply: Change ownership from driver to core")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Rhyland Klein <rklein@xxxxxxxxxx>
> ---
> v3:
>  - Changed calls to ->get_property() to use common
>    power_supply_get_property()
>  - reworded description, added "Fixes" line
>  - Changed return value of power_supply_get_property() to -EAGAIN
> 
> v2:
>  - Added cc stable
>  - changed return to -EAGAIN in case of use_cnt < 1
>  - Removed WARNING
>  - return value check added in additional patch:
>    https://lkml.org/lkml/2016/6/6/706
> 
>  drivers/power/power_supply_core.c | 26 ++++++++++++++++----------
>  1 file changed, 16 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/power/power_supply_core.c b/drivers/power/power_supply_core.c
> index 456987c88baa..cccc630bd68e 100644
> --- a/drivers/power/power_supply_core.c
> +++ b/drivers/power/power_supply_core.c
> @@ -492,7 +492,7 @@ int power_supply_get_property(struct power_supply *psy,
>  			    union power_supply_propval *val)
>  {
>  	if (atomic_read(&psy->use_cnt) <= 0)
> -		return -ENODEV;
> +		return -EAGAIN;

Wait, no. I was thinking of changing the return value in
power_supply_read_temp() if we really want EAGAIN:
ret = power_supply_get_property(...);
if (ret)
	return -EAGAIN;

On the other hand, here both return values look correct... the call can
be executed too early (not very common) or too late after unbinding the
driver (also kind of specific).

>  
>  	return psy->desc->get_property(psy, psp, val);
>  }
> @@ -564,12 +564,14 @@ static int power_supply_read_temp(struct thermal_zone_device *tzd,
>  	int ret;
>  
>  	WARN_ON(tzd == NULL);
> +
>  	psy = tzd->devdata;
> -	ret = psy->desc->get_property(psy, POWER_SUPPLY_PROP_TEMP, &val);
> +	ret = power_supply_get_property(psy, POWER_SUPPLY_PROP_TEMP, &val);
> +	if (!ret)
> +		return ret;

I think you wanted reverse:
	if (ret)

>  
>  	/* Convert tenths of degree Celsius to milli degree Celsius. */
> -	if (!ret)
> -		*temp = val.intval * 100;
> +	*temp = val.intval * 100;
>  
>  	return ret;
>  }
> @@ -612,10 +614,12 @@ static int ps_get_max_charge_cntl_limit(struct thermal_cooling_device *tcd,
>  	int ret;
>  
>  	psy = tcd->devdata;
> -	ret = psy->desc->get_property(psy,
> -		POWER_SUPPLY_PROP_CHARGE_CONTROL_LIMIT_MAX, &val);
> +	ret = power_supply_get_property(psy,
> +			POWER_SUPPLY_PROP_CHARGE_CONTROL_LIMIT_MAX, &val);
>  	if (!ret)
> -		*state = val.intval;
> +		return ret;

Wait, again - why are you inverting the logic of 'ret'?

BR,
Krzysztof

> +
> +	*state = val.intval;
>  
>  	return ret;
>  }
> @@ -628,10 +632,12 @@ static int ps_get_cur_chrage_cntl_limit(struct thermal_cooling_device *tcd,
>  	int ret;
>  
>  	psy = tcd->devdata;
> -	ret = psy->desc->get_property(psy,
> -		POWER_SUPPLY_PROP_CHARGE_CONTROL_LIMIT, &val);
> +	ret = power_supply_get_property(psy,
> +			POWER_SUPPLY_PROP_CHARGE_CONTROL_LIMIT, &val);
>  	if (!ret)
> -		*state = val.intval;
> +		return ret;
> +
> +	*state = val.intval;
>  
>  	return ret;
>  }
>