linux-kernel - Re: [PATCH] led: core: Fix race on software blink cancellation

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Message-ID: <20180208215041.GA31216@amd>
Date:   Thu, 8 Feb 2018 22:50:41 +0100
From:   Pavel Machek <pavel@....cz>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>
Cc:     linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org,
        craig.mcqueen@...errange.com.au,
        Hans de Goede <hdegoede@...hat.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Matthieu CASTET <matthieu.castet@...rot.com>,
        Dan Murphy <dmurphy@...com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Ben Whitten <ben.whitten@...il.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Andrew Lunn <andrew@...n.ch>,
        Alan Mizrahi <alan@...rahi.com.ve>,
        Vadim Pasternak <vadimp@...lanox.com>,
        David Lin <dtwlin@...gle.com>, Joel Stanley <joel@....id.au>,
        Cédric Le Goater <clg@...d.org>,
        Willy Tarreau <w@....eu>, Andrew Jeffery <andrew@...id.au>,
        Javier Martinez Canillas <javier@...hile0.org>,
        Colin King <colin.king@...onical.com>
Subject: Re: [PATCH] led: core: Fix race on software blink cancellation

Hi!

> Any comments? I'd like to have some acks before applying
> this patch.

I can't say I like it.

> > Commit d23a22a74fde ("leds: delay led_set_brightness if stopping soft-blink")
> > made a modifications to the LED core allowing for led_set_brightness() to be
> > called from hard-irq context when soft blink is being handled in soft-irq.
> > 
> > Since that time LED core has undergone modifications related to addition of
> > generic support for delegating brightness setting to a workqueue as well as
> > subsequent fixes for blink setting use cases.
> > 
> > After that the LED core code became hard to maintain and analyze, especially
> > due to the imposed hard-irq context compatibility. It also turned out that
> > in some cases a LED remained off after executing following sequence of commands:
> > 
> > 1. echo timer > trigger
> > 2. echo 0 > brightness
> > 3. echo 100 > brightness
> > 
> > The reason was LED_BLINK_DISABLE operation delegated to a set_brightness_work,
> > triggered in 2., which was handled after 3. took effect.

Could we wait for delayed work to be done before setting the
brightness to fix this one?

									Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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