[PATCH v2 0/4] leds: trigger: netdev: fix sysfs_update_group() races

[A. Sverdlin]

From: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxxxx>

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:
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)
v1:
https://lore.kernel.org/all/20260914132356.807004-1-alexander.sverdlin@xxxxxxxxxxx/

Alexander Sverdlin (4):
  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: Serialize mode/interval stores with trigger
    lock

 drivers/leds/trigger/ledtrig-netdev.c | 54 +++++++++++++++++++++------
 1 file changed, 43 insertions(+), 11 deletions(-)

-- 
2.55.0