Locking in LED core really not needed or missing?

Locking in LED core really not needed or missing?

[Heiner Kallweit]

I'm a little puzzled about the more or less completely missing locking in the LED core.

Let's just take led_timer_function as example.
It modifies led_cdev->flags and led_cdev->brightness from soft irq context
(soft blink timer) w/o locking. Accessing these fields is not guaranteed to be atomic
and the function doesn't even use set_bit etc. for modifying the bitmap.

And brightness_set and other exported functions can even be called from
hard irq context (e.g. by triggers).

This seems to be quite unsafe to me. Just think of a soft or hard irq colliding
with a sysfs access. IMHO it's just due to the fact that these collision scenarios
are relatively unlikely that we don't have problems.
Am I missing something or is this actually an open issue?

Re: Locking in LED core really not needed or missing?

[Jacek Anaszewski]

Hi Heiner,

On 01/08/2016 09:31 PM, Heiner Kallweit wrote:
> I'm a little puzzled about the more or less completely missing locking in the LED core.
>
> Let's just take led_timer_function as example.
> It modifies led_cdev->flags and led_cdev->brightness from soft irq context
> (soft blink timer) w/o locking. Accessing these fields is not guaranteed to be atomic
> and the function doesn't even use set_bit etc. for modifying the bitmap.
>
> And brightness_set and other exported functions can even be called from
> hard irq context (e.g. by triggers).

led_set_brightness() behaves differently when blink timer is enabled.
This issue was initially addressed by the patch [1].
Currently even more related improvements sit on linux-next.

> This seems to be quite unsafe to me. Just think of a soft or hard irq colliding
> with a sysfs access. IMHO it's just due to the fact that these collision scenarios
> are relatively unlikely that we don't have problems.
> Am I missing something or is this actually an open issue?
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[1] http://www.spinics.net/lists/linux-leds/msg00006.html

-- 
Best Regards,
Jacek Anaszewski