On Sat, Feb 21, 2026 at 06:01:46PM +0800, Shiji Yang wrote:

The OpenWrt community reports that sometimes devices fail to start[1]
on 5.15 kernel. After further tracking, this is caused by a AB-BA
deadlock which can be reproduced in at least 5.15, 6.6, 6.12 and latest
6.18 LTS kenrel.

Hi Shiji

Please could you test this patch. It is based on the net tree, but
with a bit of fuzz will probably apply to older trees.

Thanks
	Andrew

From bf4d66187585a1893d558cb9357f1ef63437b898 Mon Sep 17 00:00:00 2001
From: Andrew Lunn <andrew@lunn.ch>
Date: Sat, 21 Feb 2026 14:51:54 -0600
Subject: [PATCH net] net: phy: register phy led_triggers during probe to avoid
 AB-BA deadlock

There is an AB-BA deadlock when both LEDS_TRIGGER_NETDEV and
LED_TRIGGER_PHY are enabled:

[ 1362.049207] [<8054e4b8>] led_trigger_register+0x5c/0x1fc             <-- Trying to get lock "triggers_list_lock" via down_write(&triggers_list_lock);
[ 1362.054536] [<80662830>] phy_led_triggers_register+0xd0/0x234
[ 1362.060329] [<8065e200>] phy_attach_direct+0x33c/0x40c
[ 1362.065489] [<80651fc4>] phylink_fwnode_phy_connect+0x15c/0x23c
[ 1362.071480] [<8066ee18>] mtk_open+0x7c/0xba0
[ 1362.075849] [<806d714c>] __dev_open+0x280/0x2b0
[ 1362.080384] [<806d7668>] __dev_change_flags+0x244/0x24c
[ 1362.085598] [<806d7698>] dev_change_flags+0x28/0x78
[ 1362.090528] [<807150e4>] dev_ioctl+0x4c0/0x654                       <-- Hold lock "rtnl_mutex" by calling rtnl_lock();
[ 1362.094985] [<80694360>] sock_ioctl+0x2f4/0x4e0
[ 1362.099567] [<802e9c4c>] sys_ioctl+0x32c/0xd8c
[ 1362.104022] [<80014504>] syscall_common+0x34/0x58

Here LED_TRIGGER_PHY is registering LED triggers during phy_attach
while holding RTNL and then taking triggers_list_lock.

[ 1362.191101] [<806c2640>] register_netdevice_notifier+0x60/0x168      <-- Trying to get lock "rtnl_mutex" via rtnl_lock();
[ 1362.197073] [<805504ac>] netdev_trig_activate+0x194/0x1e4
[ 1362.202490] [<8054e28c>] led_trigger_set+0x1d4/0x360                 <-- Hold lock "triggers_list_lock" by down_read(&triggers_list_lock);
[ 1362.207511] [<8054eb38>] led_trigger_write+0xd8/0x14c
[ 1362.212566] [<80381d98>] sysfs_kf_bin_write+0x80/0xbc
[ 1362.217688] [<8037fcd8>] kernfs_fop_write_iter+0x17c/0x28c
[ 1362.223174] [<802cbd70>] vfs_write+0x21c/0x3c4
[ 1362.227712] [<802cc0c4>] ksys_write+0x78/0x12c
[ 1362.232164] [<80014504>] syscall_common+0x34/0x58

Here LEDS_TRIGGER_NETDEV is being enabled on an LED. It first takes
triggers_list_lock and then RTNL. A classical AB-BA deadlock.

phy_led_triggers_registers() does not require the RTNL, it does not
make any calls into the network stack which require protection. There
is also no requirement the PHY has been attached to a MAC, the
triggers only make use of phydev state. This allows the call to
phy_led_triggers_registers() to be placed elsewhere. PHY probe() and
release() don't hold RTNL, so solving the AB-BA deadlock.

Reported-by: Shiji Yang <redacted>
Closes: https://lore.kernel.org/all/OS7PR01MB13602B128BA1AD3FA38B6D1FFBC69A@OS7PR01MB13602.jpnprd01.prod.outlook.com/ (local)
Fixes: 06f502f57d0d ("leds: trigger: Introduce a NETDEV trigger")
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
---
 drivers/net/phy/phy_device.c | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index 9b8eaac63b90..cbb4af604aa5 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c

@@ -1866,8 +1866,6 @@ int phy_attach_direct(struct net_device *dev, struct phy_device *phydev,
 		goto error;
 
 	phy_resume(phydev);
-	if (!phydev->is_on_sfp_module)
-		phy_led_triggers_register(phydev);
 
 	/**
 	 * If the external phy used by current mac interface is managed by

@@ -1982,9 +1980,6 @@ void phy_detach(struct phy_device *phydev)
 	phydev->phy_link_change = NULL;
 	phydev->phylink = NULL;
 
-	if (!phydev->is_on_sfp_module)
-		phy_led_triggers_unregister(phydev);
-
 	if (phydev->mdio.dev.driver)
 		module_put(phydev->mdio.dev.driver->owner);
 

@@ -3778,16 +3773,27 @@ static int phy_probe(struct device *dev)
 	/* Set the state to READY by default */
 	phydev->state = PHY_READY;
 
+	/* Register the PHY LED triggers */
+	if (!phydev->is_on_sfp_module)
+		phy_led_triggers_register(phydev);
+
 	/* Get the LEDs from the device tree, and instantiate standard
 	 * LEDs for them.
 	 */
-	if (IS_ENABLED(CONFIG_PHYLIB_LEDS) && !phy_driver_is_genphy(phydev))
+	if (IS_ENABLED(CONFIG_PHYLIB_LEDS) && !phy_driver_is_genphy(phydev)) {
 		err = of_phy_leds(phydev);
+		if (err)
+			goto out;
+	}
+
+	return 0;
 
 out:
+	if (!phydev->is_on_sfp_module)
+		phy_led_triggers_unregister(phydev);
+
 	/* Re-assert the reset signal on error */
-	if (err)
-		phy_device_reset(phydev, 1);
+	phy_device_reset(phydev, 1);
 
 	return err;
 }

@@ -3801,6 +3807,9 @@ static int phy_remove(struct device *dev)
 	if (IS_ENABLED(CONFIG_PHYLIB_LEDS) && !phy_driver_is_genphy(phydev))
 		phy_leds_unregister(phydev);
 
+	if (!phydev->is_on_sfp_module)
+		phy_led_triggers_unregister(phydev);
+
 	phydev->state = PHY_DOWN;
 
 	phy_cleanup_ports(phydev);

-- 
2.51.0