linux-kernel - Re: [PATCH AUTOSEL for 4.14 065/110] led: core: Fix brightness setting when setting delay

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Message-ID: <20180313093703.GB27669@kroah.com>
Date:   Tue, 13 Mar 2018 10:37:03 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>
Cc:     Matthias Schiffer <mschiffer@...verse-factory.net>,
        Sasha Levin <Alexander.Levin@...rosoft.com>,
        Pavel Machek <pavel@....cz>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Matthieu CASTET <matthieu.castet@...rot.com>,
        "linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>
Subject: Re: [PATCH AUTOSEL for 4.14 065/110] led: core: Fix brightness
 setting when setting delay_off=0

On Mon, Mar 12, 2018 at 09:20:48PM +0100, Jacek Anaszewski wrote:
> On 03/12/2018 04:45 PM, Matthias Schiffer wrote:
> > On 03/12/2018 04:28 PM, Greg KH wrote:
> >> On Mon, Mar 12, 2018 at 04:00:01PM +0100, Matthias Schiffer wrote:
> >>> On 02/06/2018 09:44 PM, Jacek Anaszewski wrote:
> >>>> On 02/06/2018 03:02 AM, Sasha Levin wrote:
> >>>>> On Sun, Feb 04, 2018 at 06:17:36PM +0100, Pavel Machek wrote:
> >>>>>>
> >>>>>>>>>>> *** if brightness=0, led off
> >>>>>>>>>>> *** else apply brightness if next timer <--- timer is stop, and will never apply new setting
> >>>>>>>>>>> ** otherwise set led_set_brightness_nosleep
> >>>>>>>>>>>
> >>>>>>>>>>> To fix that, when we delete the timer, we should clear LED_BLINK_SW.
> >>>>>>>>>>
> >>>>>>>>>> Can you run the tests on the affected stable kernels? I have feeling
> >>>>>>>>>> that the problem described might not be present there.
> >>>>>>>>>
> >>>>>>>>> Hm, I don't seem to have HW to test that out. Maybe someone else does?
> >>>>>>>>
> >>>>>>>> Why are you submitting patches you have no way to test?
> >>>>>>>
> >>>>>>> What?  This is stable tree backporting, why are you trying to make a
> >>>>>>> requirement for something that we have never had before?
> >>>>>>
> >>>>>> I don't think random patches should be sent to stable just because
> >>>>>> they appeared in mainline. Plus, I don't think I'm making new rules:
> >>>>>>
> >>>>>> submit-checklist.rst:
> >>>>>>
> >>>>>> 13) Has been build- and runtime tested with and without ``CONFIG_SMP``
> >>>>>> and
> >>>>>>    ``CONFIG_PREEMPT.``
> >>>>>>
> >>>>>> stable-kernel-rules.rst:
> >>>>>>
> >>>>>> Rules on what kind of patches are accepted, and which ones are not,
> >>>>>> into the "-stable" tree:
> >>>>>>
> >>>>>> - It must be obviously correct and tested.
> >>>>>> - It must fix a real bug that bothers people (not a, "This could be a
> >>>>>>   problem..." type thing).
> >>>>>
> >>>>> So you're saying that this doesn't qualify as a bug?
> >>>>>
> >>>>>>> This is a backport of a patch that is already upstream.  If it doesn't
> >>>>>>> belong in a stable tree, great, let us know that, saying why it is so.
> >>>>>>
> >>>>>> See jacek.anaszewski@...il.com 's explanation.
> >>>>>
> >>>>> I might be missing something, but Jacek suggested I pull another patch
> >>>>> before this one?
> >>>>
> >>>> Just to clarify:
> >>>>
> >>>> For 4.14 below patches are chosen correctly:
> >>>>
> >>>> [PATCH AUTOSEL for 4.14 065/110] led: core: Fix brightness setting when
> >>>> setting delay_off=0
> >>>> [PATCH AUTOSEL for 4.14 094/110] leds: core: Fix regression caused by
> >>>> commit 2b83ff96f51d
> >>>>
> >>>> For 4.9 both above patches are needed preceded by:
> >>>>
> >>>> eb1610b4c273 ("led: core: Fix blink_brightness setting race")
> >>>>
> >>>> The issue the patch [PATCH AUTOSEL for 4.14 065/110] fixes was
> >>>> introduced in 4.7, and thus it should be removed from the series
> >>>> for 3.18 and 4.4.
> >>>>
> >>>
> >>> It seems only "led: core: Fix brightness setting when setting delay_off=0"
> >>> was applied to 4.9. Could we get the regression fixes backported to 4.9 as
> >>> well?
> >>
> >> What exact fixes were they?  I'll be glad to apply them if I have a git
> >> commit id.
> >>
> >> thanks,
> >>
> >> greg k-h
> >>
> > 
> > At least 7b6af2c531 ("leds: core: Fix regression caused by commit
> > 2b83ff96f51d") is missing, causing visible regressions (LEDs not working at
> > all) on some OpenWrt devices. This was fixed in 4.4.121 by reverting the
> > offending commit, but if I followed the discussion correctly, 4.9 should
> > get the follow-up commit 7b6af2c531 instead (like 4.14 already did).
> > 
> > Jacek's mail I replied to mentions that eb1610b4c273 ("led: core: Fix
> > blink_brightness setting race") should be included in 4.9 as well, but I
> > don't know the impact of the issue it fixes.
> 
> It doesn't fix any reported issue, but is just an improvement
> aiming at preventing potential races while changing blink brightness.
> 
> After taking closer look it turns out that for the patches in question
> to apply cleanly we need in 4.9 also a patch which introduces atomic
> bit fields for blink flags.
> 
> Effectively, here is the list of patches required in 4.9 stable:
> 
> Revert "led: core: Fix brightness setting when setting delay_off=0"
> 
> followed by:
> 
> a9c6ce57ec ("led: core: Use atomic bit-field for the blink-flags")
> eb1610b4c2 ("led: core: Fix blink_brightness setting race")
> 2b83ff96f5 ("led: core: Fix brightness setting when setting delay_off=0")
> 7b6af2c531 ("leds: core: Fix regression caused by commit 2b83ff96f51d")

Odd, I just got another report that the 4.9.87 release fixed some
reported LED issues, so why do I need all of these?

Should I just revert the single 2b83ff96f51d commit here instead?

Totally confused...

greg k-h