Re: [PATCH] leds: led-class: Only Add LED to leds_list when it is fully ready

[Lee Jones <lee@kernel.org>]

On Fri, 12 Dec 2025, Hans de Goede wrote:

> Hi,
> 
> On 12-Dec-25 07:49, Sebastian Reichel wrote:
> > Hi,
> > 
> > On Thu, Dec 11, 2025 at 05:37:27PM +0100, Hans de Goede wrote:
> >> Before this change the LED was added to leds_list before led_init_core()
> >> gets called adding it the list before led_classdev.set_brightness_work gets
> >> initialized.
> >>
> >> This leaves a window where led_trigger_register() of a LED's default
> >> trigger will call led_trigger_set() which calls led_set_brightness()
> >> which in turn will end up queueing the *uninitialized*
> >> led_classdev.set_brightness_work.
> >>
> >> This race gets hit by the lenovo-thinkpad-t14s EC driver which registers
> >> 2 LEDs with a default trigger provided by snd_ctl_led.ko in quick
> >> succession. The first led_classdev_register() causes an async modprobe of
> >> snd_ctl_led to run and that async modprobe manages to exactly hit
> >> the window where the second LED is on the leds_list without led_init_core()
> >> being called for it, resulting in:
> >>
> >>  ------------[ cut here ]------------
> >>  WARNING: CPU: 11 PID: 5608 at kernel/workqueue.c:4234 __flush_work+0x344/0x390
> >>  Hardware name: LENOVO 21N2S01F0B/21N2S01F0B, BIOS N42ET93W (2.23 ) 09/01/2025
> >>  ...
> >>  Call trace:
> >>   __flush_work+0x344/0x390 (P)
> >>   flush_work+0x2c/0x50
> >>   led_trigger_set+0x1c8/0x340
> >>   led_trigger_register+0x17c/0x1c0
> >>   led_trigger_register_simple+0x84/0xe8
> >>   snd_ctl_led_init+0x40/0xf88 [snd_ctl_led]
> >>   do_one_initcall+0x5c/0x318
> >>   do_init_module+0x9c/0x2b8
> >>   load_module+0x7e0/0x998
> >>
> >> Close the race window by moving the adding of the LED to leds_list to
> >> after the led_init_core() call.
> >>
> >> Cc: Sebastian Reichel <sre@kernel.org>
> >> Cc: stable@vger.kernel.org
> >> Signed-off-by: Hans de Goede <johannes.goede@oss.qualcomm.com>
> >> ---
> > 
> > heh, I've never hit this. But I guess that is not too surprising
> > considering it is a race condition. The change looks good to me:
> > 
> > Reviewed-by: Sebastian Reichel <sre@kernel.org>
> 
> Thx.
>  
> >> Note no Fixes tag as this problem has been around for a long long time,
> >> so I could not really find a good commit for the Fixes tag.
> > 
> > My suggestion would be:
> > 
> > Fixes: d23a22a74fde ("leds: delay led_set_brightness if stopping soft-blink")
> 
> Ack, that works for me.
> 
> Lee can you add this Fixes tag while merging ?
> 
> Also (in case it is not obvious) this is a bugfix so it would be
> nice if this could go in a fixes pull-request for 6.19.

Yes, I can add the Fixes: tag and no, I have no plans to send this for
-fixes.  As you rightly mentioned, this issue has been around for a long
time already.  I tend to only send -fixes pull-requests for things that
broke in -rc1 of the same release.

That said, however, if I end up sending one for something else, I will
try to remember to add this one to it as well.

-- 
Lee Jones [李琼斯]