[PATCH] phy: ti: tusb1210: Resolve charger-det crash if charger psy is unregistered

From: Hans de Goede <hdegoede@redhat.com>
To: Vinod Koul <vkoul@kernel.org>,
	Kishon Vijay Abraham I <kishon@kernel.org>
Cc: Hans de Goede <hdegoede@redhat.com>, linux-phy@lists.infradead.org
Subject: [PATCH] phy: ti: tusb1210: Resolve charger-det crash if charger psy is unregistered
Date: Sat,  6 Apr 2024 16:08:21 +0200	[thread overview]
Message-ID: <20240406140821.18624-1-hdegoede@redhat.com> (raw)

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: 48969a5623ed ("phy: ti: tusb1210: Add charger detection")
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
 drivers/phy/ti/phy-tusb1210.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/drivers/phy/ti/phy-tusb1210.c b/drivers/phy/ti/phy-tusb1210.c
index 13cd614e12a1..751fecd466e3 100644
--- a/drivers/phy/ti/phy-tusb1210.c
+++ b/drivers/phy/ti/phy-tusb1210.c
@@ -69,7 +69,6 @@ struct tusb1210 {
 	struct delayed_work chg_det_work;
 	struct notifier_block psy_nb;
 	struct power_supply *psy;
-	struct power_supply *charger;
 #endif
 };
 
@@ -236,19 +235,24 @@ 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;
 
-	return val.intval;
+	power_supply_put(charger);
+
+	return online;
 }
 
 static void tusb1210_chg_det_work(struct work_struct *work)
@@ -473,9 +477,6 @@ 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) { }
-- 
2.44.0


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