[PATCH v6 0/5] leds: trigger: netdev: fix sysfs_update_group() races

["A. Sverdlin" <alexander.sverdlin@siemens.com>]

From: Alexander Sverdlin <alexander.sverdlin@siemens.com>

The netdev LED trigger refreshes the link_speed attribute group with
sysfs_update_group() from several contexts (the NETDEV_CHANGE notifier,
device_name writes and, indirectly, trigger (de)activation) that share no
common lock. On a board that emits PHY link events while the trigger is
being (re)armed during boot this is observed as a hard sysfs failure:

  sysfs: cannot create duplicate filename '...green:lan/link_10'
  ...
  led_trigger_set
  led_trigger_write

The window between activate() and device_add_groups() in led_trigger_set()
is narrow, so to reproduce it reliably I artificially widened it with the
debug patch below:

--- a/drivers/leds/led-triggers.c
+++ b/drivers/leds/led-triggers.c
@@ -12,6 +12,7 @@
 #include <linux/list.h>
 #include <linux/spinlock.h>
 #include <linux/device.h>
+#include <linux/delay.h>
 #include <linux/timer.h>
 #include <linux/rwsem.h>
 #include <linux/leds.h>
@@ -223,6 +224,8 @@ int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
 		if (ret)
 			goto err_activate;

+		msleep(5000);
+
 		ret = device_add_groups(led_cdev->dev, trig->groups);
 		if (ret) {
 			dev_err(led_cdev->dev, "Failed to add trigger attributes\n");

With that msleep() in place, writing the trigger while a NETDEV_CHANGE is
delivered from the linkwatch workqueue reproduces the duplicate-filename
splat every time.

The whole series is LOCKDEP-verified.

Changelog:
v6:
- report invalid interval to user space
- fixed unlocked hw_control check in interval_store()
- added missing carrier_link_up check in netdev_trig_sw_blink()
v5:
- removed unset_device_name()
- https://lore.kernel.org/all/20261020124651.1987272-1-alexander.sverdlin@siemens.com/
v4:
- introduced netdev_trig_sw_blink() and used it in netdev_trig_work()
- https://lore.kernel.org/all/20261001131206.2513248-1-alexander.sverdlin@siemens.com/
v3:
- introduced unset_device_name() as a counterpart of set_device_name()
- guard() has been converted to either explicit mutex_lock()/mutex_unlock()
  or scoped_guard()
- rebased onto next-20260925
- https://lore.kernel.org/all/20260929120902.2793138-1-alexander.sverdlin@siemens.com/
v2:
- addressed pre-existing issues found by Sashiko (patches 1&2)
- reduced verbosity both in comments and in commit messages
- patch 3 is a combined rework of patches 1&2 from v1
- dropped sync from cancel_delayed_work() (worker now takes the lock)
- https://lore.kernel.org/all/20260921093249.3481413-1-alexander.sverdlin@siemens.com/
v1:
- https://lore.kernel.org/all/20260914132356.807004-1-alexander.sverdlin@siemens.com/


Alexander Sverdlin (5):
  leds: trigger: netdev: Put netdev on activate error path
  leds: trigger: netdev: Access net_dev under trigger_data->lock in the
    worker
  leds: trigger: netdev: Fix sysfs_update_group() races
  leds: trigger: netdev: Report invalid interval to user space
  leds: trigger: netdev: Serialize mode/interval stores with trigger
    lock

 drivers/leds/trigger/ledtrig-netdev.c | 140 ++++++++++++++++++--------
 1 file changed, 96 insertions(+), 44 deletions(-)

-- 
2.56.0