power: supply: bq27xxx: Fix poll_interval handling and races on remove

Before this patch bq27xxx_battery_teardown() was setting poll_interval = 0
to avoid bq27xxx_battery_update() requeuing the delayed_work item.

There are 2 problems with this:

1. If the driver is unbound through sysfs, rather then the module being
   rmmod-ed, this changes poll_interval unexpectedly

2. This is racy, after it being set poll_interval could be changed
   before bq27xxx_battery_update() checks it through
   /sys/module/bq27xxx_battery/parameters/poll_interval

Fix this by added a removed attribute to struct bq27xxx_device_info and
using that instead of setting poll_interval to 0.

There also is another poll_interval related race on remove(), writing
/sys/module/bq27xxx_battery/parameters/poll_interval will requeue
the delayed_work item for all devices on the bq27xxx_battery_devices
list and the device being removed was only removed from that list
after cancelling the delayed_work item.

Fix this by moving the removal from the bq27xxx_battery_devices list
to before cancelling the delayed_work item.

Fixes: 8cfaaa8 ("bq27x00_battery: Fix OOPS caused by unregistring bq27x00 driver")
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

@@ -1801,7 +1801,7 @@ static void bq27xxx_battery_update_unlocked(struct bq27xxx_device_info *di)
 
 	di->last_update = jiffies;
 
-	if (poll_interval > 0)
+	if (!di->removed && poll_interval > 0)
 		mod_delayed_work(system_wq, &di->work, poll_interval * HZ);
 }
 
@@ -2132,22 +2132,18 @@ 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);
-
 	mutex_lock(&bq27xxx_list_lock);
 	list_del(&di->list);
 	mutex_unlock(&bq27xxx_list_lock);
 
+	/* Set removed to avoid bq27xxx_battery_update() re-queuing the work */
+	mutex_lock(&di->lock);
+	di->removed = true;
+	mutex_unlock(&di->lock);
+
+	cancel_delayed_work_sync(&di->work);
+
+	power_supply_unregister(di->bat);
 	mutex_destroy(&di->lock);
 }
 EXPORT_SYMBOL_GPL(bq27xxx_battery_teardown);

include/linux/power/bq27xxx_battery.h

@@ -68,6 +68,7 @@ struct bq27xxx_device_info {
 	struct bq27xxx_access_methods bus;
 	struct bq27xxx_reg_cache cache;
 	int charge_design_full;
+	bool removed;
 	unsigned long last_update;
 	struct delayed_work work;
 	struct power_supply *bat;