When working on LED support for r8169 I got the following lockdep
warning. Easiest way to prevent this scenario seems to be to take
the RTNL lock before the trigger_data lock in set_device_name().
======================================================
WARNING: possible circular locking dependency detected
6.7.0-rc2-next-20231124+ #2 Not tainted
------------------------------------------------------
bash/383 is trying to acquire lock:
ffff888103aa1c68 (&trigger_data->lock){+.+.}-{3:3}, at: netdev_trig_notify+0xec/0x190 [ledtrig_netdev]
but task is already holding lock:
ffffffff8cddf808 (rtnl_mutex){+.+.}-{3:3}, at: rtnl_lock+0x12/0x20
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (rtnl_mutex){+.+.}-{3:3}:
__mutex_lock+0x9b/0xb50
mutex_lock_nested+0x16/0x20
rtnl_lock+0x12/0x20
set_device_name+0xa9/0x120 [ledtrig_netdev]
netdev_trig_activate+0x1a1/0x230 [ledtrig_netdev]
led_trigger_set+0x172/0x2c0
led_trigger_write+0xf1/0x140
sysfs_kf_bin_write+0x5d/0x80
kernfs_fop_write_iter+0x15d/0x210
vfs_write+0x1f0/0x510
ksys_write+0x6c/0xf0
__x64_sys_write+0x14/0x20
do_syscall_64+0x3f/0xf0
entry_SYSCALL_64_after_hwframe+0x6c/0x74
-> #0 (&trigger_data->lock){+.+.}-{3:3}:
__lock_acquire+0x1459/0x25a0
lock_acquire+0xc8/0x2d0
__mutex_lock+0x9b/0xb50
mutex_lock_nested+0x16/0x20
netdev_trig_notify+0xec/0x190 [ledtrig_netdev]
call_netdevice_register_net_notifiers+0x5a/0x100
register_netdevice_notifier+0x85/0x120
netdev_trig_activate+0x1d4/0x230 [ledtrig_netdev]
led_trigger_set+0x172/0x2c0
led_trigger_write+0xf1/0x140
sysfs_kf_bin_write+0x5d/0x80
kernfs_fop_write_iter+0x15d/0x210
vfs_write+0x1f0/0x510
ksys_write+0x6c/0xf0
__x64_sys_write+0x14/0x20
do_syscall_64+0x3f/0xf0
entry_SYSCALL_64_after_hwframe+0x6c/0x74
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(rtnl_mutex);
lock(&trigger_data->lock);
lock(rtnl_mutex);
lock(&trigger_data->lock);
*** DEADLOCK ***
8 locks held by bash/383:
#0: ffff888103ff33f0 (sb_writers#3){.+.+}-{0:0}, at: ksys_write+0x6c/0xf0
#1: ffff888103aa1e88 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_write_iter+0x114/0x210
#2: ffff8881036f1890 (kn->active#82){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x11d/0x210
#3: ffff888108e2c358 (&led_cdev->led_access){+.+.}-{3:3}, at: led_trigger_write+0x30/0x140
#4: ffffffff8cdd9e10 (triggers_list_lock){++++}-{3:3}, at: led_trigger_write+0x75/0x140
#5: ffff888108e2c270 (&led_cdev->trigger_lock){++++}-{3:3}, at: led_trigger_write+0xe3/0x140
#6: ffffffff8cdde3d0 (pernet_ops_rwsem){++++}-{3:3}, at: register_netdevice_notifier+0x1c/0x120
#7: ffffffff8cddf808 (rtnl_mutex){+.+.}-{3:3}, at: rtnl_lock+0x12/0x20
stack backtrace:
CPU: 0 PID: 383 Comm: bash Not tainted 6.7.0-rc2-next-20231124+ #2
Hardware name: Default string Default string/Default string, BIOS ADLN.M6.SODIMM.ZB.CY.015 08/08/2023
Call Trace:
<TASK>
dump_stack_lvl+0x5c/0xd0
dump_stack+0x10/0x20
print_circular_bug+0x2dd/0x410
check_noncircular+0x131/0x150
__lock_acquire+0x1459/0x25a0
lock_acquire+0xc8/0x2d0
? netdev_trig_notify+0xec/0x190 [ledtrig_netdev]
__mutex_lock+0x9b/0xb50
? netdev_trig_notify+0xec/0x190 [ledtrig_netdev]
? __this_cpu_preempt_check+0x13/0x20
? netdev_trig_notify+0xec/0x190 [ledtrig_netdev]
? __cancel_work_timer+0x11c/0x1b0
? __mutex_lock+0x123/0xb50
mutex_lock_nested+0x16/0x20
? mutex_lock_nested+0x16/0x20
netdev_trig_notify+0xec/0x190 [ledtrig_netdev]
call_netdevice_register_net_notifiers+0x5a/0x100
register_netdevice_notifier+0x85/0x120
netdev_trig_activate+0x1d4/0x230 [ledtrig_netdev]
led_trigger_set+0x172/0x2c0
? preempt_count_add+0x49/0xc0
led_trigger_write+0xf1/0x140
sysfs_kf_bin_write+0x5d/0x80
kernfs_fop_write_iter+0x15d/0x210
vfs_write+0x1f0/0x510
ksys_write+0x6c/0xf0
__x64_sys_write+0x14/0x20
do_syscall_64+0x3f/0xf0
entry_SYSCALL_64_after_hwframe+0x6c/0x74
RIP: 0033:0x7f269055d034
Code: c7 00 16 00 00 00 b8 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 80 3d 35 c3 0d 00 00 74 13 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 54 c3 0f 1f 00 48 83 ec 28 48 89 54 24 18 48
RSP: 002b:00007ffddb7ef748 EFLAGS: 00000202 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000007 RCX: 00007f269055d034
RDX: 0000000000000007 RSI: 000055bf5f4af3c0 RDI: 0000000000000001
RBP: 000055bf5f4af3c0 R08: 0000000000000073 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000007
R13: 00007f26906325c0 R14: 00007f269062ff20 R15: 0000000000000000
</TASK>
Fixes: f42c437acc55 ("leds: trigger: netdev: add additional specific link speed mode")
Signed-off-by: Heiner Kallweit <hkallweit1@xxxxxxxxx>
---
drivers/leds/trigger/ledtrig-netdev.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/drivers/leds/trigger/ledtrig-netdev.c b/drivers/leds/trigger/ledtrig-netdev.c
index e358e77e4..4dbcb2573 100644
--- a/drivers/leds/trigger/ledtrig-netdev.c
+++ b/drivers/leds/trigger/ledtrig-netdev.c
@@ -226,6 +226,11 @@ static int set_device_name(struct led_netdev_data *trigger_data,
cancel_delayed_work_sync(&trigger_data->work);
+ /*
+ * Take RTNL lock before trigger_data lock to prevent potential
+ * deadlock with netdev notifier registration.
+ */
+ rtnl_lock();
mutex_lock(&trigger_data->lock);
if (trigger_data->net_dev) {
@@ -245,16 +250,14 @@ static int set_device_name(struct led_netdev_data *trigger_data,
trigger_data->carrier_link_up = false;
trigger_data->link_speed = SPEED_UNKNOWN;
trigger_data->duplex = DUPLEX_UNKNOWN;
- if (trigger_data->net_dev != NULL) {
- rtnl_lock();
+ if (trigger_data->net_dev)
get_device_state(trigger_data);
- rtnl_unlock();
- }
trigger_data->last_activity = 0;
set_baseline_state(trigger_data);
mutex_unlock(&trigger_data->lock);
+ rtnl_unlock();
return 0;
}
--
2.43.0
