phy: ti: tusb1210: Resolve charger-det crash if charger psy is unregi…

…stered

[ Upstream commit bf6e4ee ]

The power_supply frame-work is not really designed for there to be
long living in kernel references to power_supply devices.

Specifically unregistering a power_supply while some other code has
a reference to it triggers a WARN in power_supply_unregister():

	WARN_ON(atomic_dec_return(&psy->use_cnt));

Folllowed by the power_supply still getting removed and the
backing data freed anyway, leaving the tusb1210 charger-detect code
with a dangling reference, resulting in a crash the next time
tusb1210_get_online() is called.

Fix this by only holding the reference in tusb1210_get_online()
freeing it at the end of the function. Note this still leaves
a theoretical race window, but it avoids the issue when manually
rmmod-ing the charger chip driver during development.

Fixes: 48969a5 ("phy: ti: tusb1210: Add charger detection")
Signed-off-by: Hans de Goede <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Vinod Koul <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>

drivers/phy/ti/phy-tusb1210.c

@@ -64,7 +64,6 @@ struct tusb1210 {
 	struct delayed_work chg_det_work;
 	struct notifier_block psy_nb;
 	struct power_supply *psy;
-	struct power_supply *charger;
 #endif
 };
 
@@ -230,19 +229,24 @@ static const char * const tusb1210_chargers[] = {
 
 static bool tusb1210_get_online(struct tusb1210 *tusb)
 {
+	struct power_supply *charger = NULL;
 	union power_supply_propval val;
-	int i;
+	bool online = false;
+	int i, ret;
 
-	for (i = 0; i < ARRAY_SIZE(tusb1210_chargers) && !tusb->charger; i++)
-		tusb->charger = power_supply_get_by_name(tusb1210_chargers[i]);
+	for (i = 0; i < ARRAY_SIZE(tusb1210_chargers) && !charger; i++)
+		charger = power_supply_get_by_name(tusb1210_chargers[i]);
 
-	if (!tusb->charger)
+	if (!charger)
 		return false;
 
-	if (power_supply_get_property(tusb->charger, POWER_SUPPLY_PROP_ONLINE, &val))
-		return false;
+	ret = power_supply_get_property(charger, POWER_SUPPLY_PROP_ONLINE, &val);
+	if (ret == 0)
+		online = val.intval;
+
+	power_supply_put(charger);
 
-	return val.intval;
+	return online;
 }
 
 static void tusb1210_chg_det_work(struct work_struct *work)
@@ -466,9 +470,6 @@ static void tusb1210_remove_charger_detect(struct tusb1210 *tusb)
 		cancel_delayed_work_sync(&tusb->chg_det_work);
 		power_supply_unregister(tusb->psy);
 	}
-
-	if (tusb->charger)
-		power_supply_put(tusb->charger);
 }
 #else
 static void tusb1210_probe_charger_detect(struct tusb1210 *tusb) { }