linux-kernel - Re: linux-stable 6.1.53 kernel crash on COLOR_ID

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Message-ID: <20230918161133.4c32a0e6@dellmb>
Date:   Mon, 18 Sep 2023 16:11:33 +0200
From:   Marek Behún <kabel@...nel.org>
To:     Pavel Machek <pavel@....cz>
Cc:     Da Xue <da@...re.computer>, lee@...nel.org, sashal@...nel.org,
        linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-stable <stable@...r.kernel.org>
Subject: Re: linux-stable 6.1.53 kernel crash on COLOR_ID_MULTI handling
 change

On Thu, 14 Sep 2023 12:21:09 +0200
Pavel Machek <pavel@....cz> wrote:

> Hi!
> 
> > We have running systems that use COLOR_ID_MULTI. The GPIO toggles
> > between two colors and we have used the identifier. RGB is not a good
> > fit since it is not a RGB LED. Please provide guidance.
> > 
> > This patch causes the system to not start: f741121a2251 leds: Fix
> > BUG_ON check for LED_COLOR_ID_MULTI that is always false
> > 
> > It was also backported to stable causing previously booting systems to
> > no longer boot.  
> 
> Lets cc patch authors.
> 
> And please drop this from stable, it does not belong there.
> 
> Best regards,
> 								Pavel

The BUG_ON was a no-op since it was introduced. It's purpose was to
prevent people from using LED_COLOR_ID_MULTI since it was thought that
non-RGB LEDs are not yet completely agreed on, or something.

But since the BUG_ON was a no-op, someone started using
LED_COLOR_ID_MULTI without noticing that they should not. There are now
even some in-tree device-tree files using LED_COLOR_ID_MULTI.

My patch that fixes the BUG_ON uncovered this and caused a regression
for some people.

I think we have to drop the BUG_ON altoghether now.

I've sent a patch to linux-leds doing just that.

Sorry for the incovenience.

Marek