[PATCH net] net: phy: skip LED triggers on PHYs on SFP modules

From: Daniel Golle
Date: Mon Dec 11 2023 - 19:06:12 EST

Calling led_trigger_register() when attaching a PHY located on an SFP
module potentially (and practically) leads into a deadlock.
Fix this by not calling led_trigger_register() for PHYs localted on SFP
modules as such modules actually never got any LEDs.

======================================================
WARNING: possible circular locking dependency detected
6.7.0-rc4-next-20231208+ #0 Tainted: G O
------------------------------------------------------
kworker/u8:2/43 is trying to acquire lock:
ffffffc08108c4e8 (triggers_list_lock){++++}-{3:3}, at: led_trigger_register+0x4c/0x1a8

but task is already holding lock:
ffffff80c5c6f318 (&sfp->sm_mutex){+.+.}-{3:3}, at: cleanup_module+0x2ba8/0x3120 [sfp]

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #3 (&sfp->sm_mutex){+.+.}-{3:3}:
__mutex_lock+0x88/0x7a0
mutex_lock_nested+0x20/0x28
cleanup_module+0x2ae0/0x3120 [sfp]
sfp_register_bus+0x5c/0x9c
sfp_register_socket+0x48/0xd4
cleanup_module+0x271c/0x3120 [sfp]
platform_probe+0x64/0xb8
really_probe+0x17c/0x3c0
__driver_probe_device+0x78/0x164
driver_probe_device+0x3c/0xd4
__driver_attach+0xec/0x1f0
bus_for_each_dev+0x60/0xa0
driver_attach+0x20/0x28
bus_add_driver+0x108/0x208
driver_register+0x5c/0x118
__platform_driver_register+0x24/0x2c
init_module+0x28/0xa7c [sfp]
do_one_initcall+0x70/0x2ec
do_init_module+0x54/0x1e4
load_module+0x1b78/0x1c8c
__do_sys_init_module+0x1bc/0x2cc
__arm64_sys_init_module+0x18/0x20
invoke_syscall.constprop.0+0x4c/0xdc
do_el0_svc+0x3c/0xbc
el0_svc+0x34/0x80
el0t_64_sync_handler+0xf8/0x124
el0t_64_sync+0x150/0x154

-> #2 (rtnl_mutex){+.+.}-{3:3}:
__mutex_lock+0x88/0x7a0
mutex_lock_nested+0x20/0x28
rtnl_lock+0x18/0x20
set_device_name+0x30/0x130
netdev_trig_activate+0x13c/0x1ac
led_trigger_set+0x118/0x234
led_trigger_write+0x104/0x17c
sysfs_kf_bin_write+0x64/0x80
kernfs_fop_write_iter+0x128/0x1b4
vfs_write+0x178/0x2a4
ksys_write+0x58/0xd4
__arm64_sys_write+0x18/0x20
invoke_syscall.constprop.0+0x4c/0xdc
do_el0_svc+0x3c/0xbc
el0_svc+0x34/0x80
el0t_64_sync_handler+0xf8/0x124
el0t_64_sync+0x150/0x154

-> #1 (&led_cdev->trigger_lock){++++}-{3:3}:
down_write+0x4c/0x13c
led_trigger_write+0xf8/0x17c
sysfs_kf_bin_write+0x64/0x80
kernfs_fop_write_iter+0x128/0x1b4
vfs_write+0x178/0x2a4
ksys_write+0x58/0xd4
__arm64_sys_write+0x18/0x20
invoke_syscall.constprop.0+0x4c/0xdc
do_el0_svc+0x3c/0xbc
el0_svc+0x34/0x80
el0t_64_sync_handler+0xf8/0x124
el0t_64_sync+0x150/0x154

-> #0 (triggers_list_lock){++++}-{3:3}:
__lock_acquire+0x12a0/0x2014
lock_acquire+0x100/0x2ac
down_write+0x4c/0x13c
led_trigger_register+0x4c/0x1a8
phy_led_triggers_register+0x9c/0x214
phy_attach_direct+0x154/0x36c
phylink_attach_phy+0x30/0x60
phylink_sfp_connect_phy+0x140/0x510
sfp_add_phy+0x34/0x50
init_module+0x15c/0xa7c [sfp]
cleanup_module+0x1d94/0x3120 [sfp]
cleanup_module+0x2bb4/0x3120 [sfp]
process_one_work+0x1f8/0x4ec
worker_thread+0x1e8/0x3d8
kthread+0x104/0x110
ret_from_fork+0x10/0x20

other info that might help us debug this:

Chain exists of:
triggers_list_lock --> rtnl_mutex --> &sfp->sm_mutex

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&sfp->sm_mutex);
lock(rtnl_mutex);
lock(&sfp->sm_mutex);
lock(triggers_list_lock);

*** DEADLOCK ***

4 locks held by kworker/u8:2/43:
#0: ffffff80c000f938 ((wq_completion)events_power_efficient){+.+.}-{0:0}, at: process_one_work+0x150/0x4ec
#1: ffffffc08214bde8 ((work_completion)(&(&sfp->timeout)->work)){+.+.}-{0:0}, at: process_one_work+0x150/0x4ec
#2: ffffffc0810902f8 (rtnl_mutex){+.+.}-{3:3}, at: rtnl_lock+0x18/0x20
#3: ffffff80c5c6f318 (&sfp->sm_mutex){+.+.}-{3:3}, at: cleanup_module+0x2ba8/0x3120 [sfp]

stack backtrace:
CPU: 0 PID: 43 Comm: kworker/u8:2 Tainted: G O 6.7.0-rc4-next-20231208+ #0
Hardware name: Bananapi BPI-R4 (DT)
Workqueue: events_power_efficient cleanup_module [sfp]
Call trace:
dump_backtrace+0xa8/0x10c
show_stack+0x14/0x1c
dump_stack_lvl+0x5c/0xa0
dump_stack+0x14/0x1c
print_circular_bug+0x328/0x430
check_noncircular+0x124/0x134
__lock_acquire+0x12a0/0x2014
lock_acquire+0x100/0x2ac
down_write+0x4c/0x13c
led_trigger_register+0x4c/0x1a8
phy_led_triggers_register+0x9c/0x214
phy_attach_direct+0x154/0x36c
phylink_attach_phy+0x30/0x60
phylink_sfp_connect_phy+0x140/0x510
sfp_add_phy+0x34/0x50
init_module+0x15c/0xa7c [sfp]
cleanup_module+0x1d94/0x3120 [sfp]
cleanup_module+0x2bb4/0x3120 [sfp]
process_one_work+0x1f8/0x4ec
worker_thread+0x1e8/0x3d8
kthread+0x104/0x110
ret_from_fork+0x10/0x20

Signed-off-by: Daniel Golle <daniel@xxxxxxxxxxxxxx>
---
drivers/net/phy/phy_device.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index d2caa89bf1fb8..08b87d7396eb9 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -1558,7 +1558,8 @@ int phy_attach_direct(struct net_device *dev, struct phy_device *phydev,
goto error;

phy_resume(phydev);
- phy_led_triggers_register(phydev);
+ if (!phydev->is_on_sfp_module)
+ phy_led_triggers_register(phydev);

/**
* If the external phy used by current mac interface is managed by
@@ -1827,7 +1828,8 @@ void phy_detach(struct phy_device *phydev)
}
phydev->phylink = NULL;

- phy_led_triggers_unregister(phydev);
+ if (!phydev->is_on_sfp_module)
+ phy_led_triggers_unregister(phydev);

if (phydev->mdio.dev.driver)
module_put(phydev->mdio.dev.driver->owner);
--
2.43.0