[PATCH 6.18 168/314] net: phy: register phy led_triggers during probe to avoid AB-BA deadlock

Sasha Levin
2026-03-10T11:27:20Z

From: Andrew Lunn <andrew@lunn.ch>

commit c8dbdc6e380e7e96a51706db3e4b7870d8a9402d upstream.

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 <yangshiji66@outlook.com>
Closes: https://lore.kernel.org/all/OS7PR01MB13602B128BA1AD3FA38B6D1FFBC69A@OS7PR01MB13602.jpnprd01.prod.outlook.com/
Fixes: 06f502f57d0d ("leds: trigger: Introduce a NETDEV trigger")
Cc: stable@vger.kernel.org
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Shiji Yang <yangshiji66@outlook.com>
Link: https://patch.msgid.link/20260222152601.1978655-1-andrew@lunn.ch
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
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 7a67c900e79a5..2353d6eced68d 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -1751,8 +1751,6 @@ 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
@@ -1867,9 +1865,6 @@ 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);

@@ -3500,16 +3495,27 @@ 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;
}
@@ -3523,6 +3529,9 @@ 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;

sfp_bus_del_upstream(phydev->sfp_bus);
--
2.51.0