Re: [PATCH] leds: trigger: Call synchronize_rcu() before calling trig->activate()

[Lee Jones <lee@kernel.org>]

On Tue, 07 May 2024, Hans de Goede wrote:

> Some triggers call led_trigger_event() from their activate() callback
> to initialize the brightness of the LED for which the trigger is being
> activated.
> 
> In order for the LEDs initial state to be set correctly this requires that
> the led_trigger_event() call uses the new version of trigger->led_cdevs,
> which has the new LED.
> 
> AFAICT led_trigger_event() will always use the new version when it is
> running on the same CPU as where the list_add_tail_rcu() call was made,
> which is why the missing synchronize_rcu() has not lead to bug reports.
> But if activate() is pre-empted, sleeps or uses a worker then
> the led_trigger_event() call may run on another CPU which may still use
> the old trigger->led_cdevs list.
> 
> Add a synchronize_rcu() call to ensure that any led_trigger_event() calls
> done from activate() always use the new list.
> 
> Triggers using led_trigger_event() from their activate() callback are:
> net/bluetooth/leds.c, net/rfkill/core.c and drivers/tty/vt/keyboard.c.
> 
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> ---
>  drivers/leds/led-triggers.c | 7 +++++++
>  1 file changed, 7 insertions(+)

Looks like there have been a few changes to led_trigger_set() since this
was authored.  Please rebase and resubmit.  Thanks.

-- 
Lee Jones [李琼斯]