linux-kernel - Re: 3.17-rc1: leds blink workqueue causes sleeping BUGs

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Message-ID: <20140825212324.GC3070@type.youpi.perso.aquilenet.fr>
Date:	Mon, 25 Aug 2014 23:23:24 +0200
From:	Samuel Thibault <samuel.thibault@...-lyon.org>
To:	Sabrina Dubroca <sd@...asysnail.net>
Cc:	Valdis.Kletnieks@...edu, Hugh Dickins <hughd@...gle.com>,
	Vincent Donnefort <vdonnefort@...il.com>,
	Bryan Wu <cooloney@...il.com>, linux-leds@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org
Subject: Re: 3.17-rc1: leds blink workqueue causes sleeping BUGs

Hello,

Sabrina Dubroca, le Mon 25 Aug 2014 23:13:40 +0200, a écrit :
> 2014-08-19, 13:06:07 -0400, Valdis.Kletnieks@...edu wrote:
> > On Sat, 16 Aug 2014 20:27:01 -0700, Hugh Dickins said:
> > > Can we safely revert your 8b37e1bef5a6 ("leds: convert blink timer to
> > > workqueue"), or have there been other changes which now depend upon it?
> > 
> > I suspect there's something else busted.  I hand-reverted that patch, and I *still*
> > see the following lockdep whine that looks related (as it talks about
> > leddev_list_lock).  next-0811 was OK, looks like next-0815 and -0818 had this....
> 
> I had a look at the code, led_trigger_event calls vt_led_set, which
> calls led_trigger_event again.

Yes, that is expected: the vt::* leds actually generate the
corresponding vt-* trigger events, which are used by the various
input*::* leds. We could indeed have a loop if the user was making the
VT::* leds use the vt-* trigger, but otherwise it's safe since it's a
different trigger. We can add code to prevent the user from building
loops, but otherwise it's a false positive.

Samuel
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