[PATCH] power_supply: power_supply_read_temp only if use_cnt > 0

[Rhyland Klein]

Add check to power_supply_read_temp() to only use the power_supply
get_property() callback if the use_cnt 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

Signed-off-by: Rhyland Klein <rklein@xxxxxxxxxx>
---
 drivers/power/power_supply_core.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/power/power_supply_core.c b/drivers/power/power_supply_core.c
index 456987c88baa..070fec621d66 100644
--- a/drivers/power/power_supply_core.c
+++ b/drivers/power/power_supply_core.c
@@ -561,11 +561,16 @@ static int power_supply_read_temp(struct thermal_zone_device *tzd,
 {
 	struct power_supply *psy;
 	union power_supply_propval val;
-	int ret;
+	int ret = 0;
 
 	WARN_ON(tzd == NULL);
+
 	psy = tzd->devdata;
-	ret = psy->desc->get_property(psy, POWER_SUPPLY_PROP_TEMP, &val);
+	WARN_ON(atomic_read(&psy->use_cnt) == 0);
+
+	if (atomic_read(&psy->use_cnt) > 0)
+		ret = psy->desc->get_property(psy, POWER_SUPPLY_PROP_TEMP,
+					      &val);
 
 	/* Convert tenths of degree Celsius to milli degree Celsius. */
 	if (!ret)
-- 
1.9.1