power: supply: bq27xxx: Fix bq27xxx_battery_update() race condition

bq27xxx_battery_update() assumes / requires that it is only run once,
not multiple times at the same time. But there are 3 possible callers:

1. bq27xxx_battery_poll() delayed_work item handler
2. bq27xxx_battery_irq_handler_thread() I2C IRQ handler
3. bq27xxx_battery_setup()

And there is no protection against these racing with each other,
fix this race condition by making all callers take di->lock:

- Rename bq27xxx_battery_update() to bq27xxx_battery_update_unlocked()

- Add new bq27xxx_battery_update() which takes di->lock and then calls
  bq27xxx_battery_update_unlocked()

- Make stale cache check code in bq27xxx_battery_get_property(), which
  already takes di->lock directly to check the jiffies, call
  bq27xxx_battery_update_unlocked() instead of messing with
  the delayed_work item

- Make bq27xxx_battery_update_unlocked() mod the delayed-work item
  so that the next poll is delayed to poll_interval milliseconds after
  the last update independent of the source of the update

Fixes: 740b755 ("bq27x00: Poll battery state")
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

Author: jwrdegoede

drivers/power/supply/bq27xxx_battery.c

@@ -1761,7 +1761,7 @@ static int bq27xxx_battery_read_health(struct bq27xxx_device_info *di)
 	return POWER_SUPPLY_HEALTH_GOOD;
 }
 
-void bq27xxx_battery_update(struct bq27xxx_device_info *di)
+static void bq27xxx_battery_update_unlocked(struct bq27xxx_device_info *di)
 {
 	struct bq27xxx_reg_cache cache = {0, };
 	bool has_singe_flag = di->opts & BQ27XXX_O_ZERO;
@@ -1800,6 +1800,16 @@ void bq27xxx_battery_update(struct bq27xxx_device_info *di)
 		di->cache = cache;
 
 	di->last_update = jiffies;
+
+	if (poll_interval > 0)
+		mod_delayed_work(system_wq, &di->work, poll_interval * HZ);
+}
+
+void bq27xxx_battery_update(struct bq27xxx_device_info *di)
+{
+	mutex_lock(&di->lock);
+	bq27xxx_battery_update_unlocked(di);
+	mutex_unlock(&di->lock);
 }
 EXPORT_SYMBOL_GPL(bq27xxx_battery_update);
 
@@ -1810,9 +1820,6 @@ static void bq27xxx_battery_poll(struct work_struct *work)
 				     work.work);
 
 	bq27xxx_battery_update(di);
-
-	if (poll_interval > 0)
-		schedule_delayed_work(&di->work, poll_interval * HZ);
 }
 
 static bool bq27xxx_battery_is_full(struct bq27xxx_device_info *di, int flags)
@@ -1985,10 +1992,8 @@ static int bq27xxx_battery_get_property(struct power_supply *psy,
 	struct bq27xxx_device_info *di = power_supply_get_drvdata(psy);
 
 	mutex_lock(&di->lock);
-	if (time_is_before_jiffies(di->last_update + 5 * HZ)) {
-		cancel_delayed_work_sync(&di->work);
-		bq27xxx_battery_poll(&di->work.work);
-	}
+	if (time_is_before_jiffies(di->last_update + 5 * HZ))
+		bq27xxx_battery_update_unlocked(di);
 	mutex_unlock(&di->lock);
 
 	if (psp != POWER_SUPPLY_PROP_PRESENT && di->cache.flags < 0)