linux-kernel - Re: [PATCH v3] power_supply: power_supply_read_temp only if use

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Date:	Wed, 8 Jun 2016 11:26:26 -0400
From:	Rhyland Klein <rklein@...dia.com>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Sebastian Reichel <sre@...nel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	David Woodhouse <dwmw2@...radead.org>
CC:	<linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Jon Hunter <jonathanh@...dia.com>, <stable@...r.kernel.org>
Subject: Re: [PATCH v3] power_supply: power_supply_read_temp only if use_cnt >
 0

On 6/8/2016 2:35 AM, Krzysztof Kozlowski wrote:
> 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@...r.kernel.org
>> Signed-off-by: Rhyland Klein <rklein@...dia.com>
>> ---
>> 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).

I did have it that way, but it seemed a little weird to me, since both
situations use the same condition (use_cnt <= 0) to trigger. I don't
think we can differentiate, unless I missed something, so I'm not sure
if it makes sense to override the return value after calling
power_supply_get_property() or not.

If I overrode the return value in get_temp, then assuming it was called
after unbinding, it would return the wrong thing (-EAGAIN). If we want
to support both EAGAIN and ENODEV, then maybe we need to use some
additional check to know which to return from power_supply_get_property().

> 
>>  
>>  	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)
> 

Indeed.

>>  
>>  	/* 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'?a
> 

copy/paste error repeated... <sigh>

-rhyland
-- 
nvpublic