linux-kernel - Re: commit 66c1ca breaks fbdev mode switching

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Date:	Tue, 7 Apr 2009 11:54:44 +0200
From:	Andrea Righi <righi.andrea@...il.com>
To:	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>
Cc:	Krzysztof Helt <krzysztof.h1@...zta.fm>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Andrey Borzenkov <arvidjaar@...il.com>,
	"Antonino A. Daplas" <adaplas@...il.com>,
	Linux Frame Buffer Device Development 
	<linux-fbdev-devel@...ts.sourceforge.net>,
	linux-pm@...ts.linux-foundation.org,
	Linux Kernel Development <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>,
	Harvey Harrison <harvey.harrison@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Stefan Richter <stefanr@...6.in-berlin.de>
Subject: Re: commit 66c1ca breaks fbdev mode switching

On Tue, Apr 07, 2009 at 11:17:00AM +0200, Geert Uytterhoeven wrote:
> On Mon, 6 Apr 2009, Andrea Righi wrote:
> > On Mon, Apr 06, 2009 at 08:47:18PM +0200, Krzysztof Helt wrote:
> > > The commit 66c1ca breaks fbdev mode switching. The first mode
> > > (selected with mode_option or during boot) is ok but every mode
> > > switch with fbset locks up computer. If the commit is reverted
> > > mode switching works correctly.
> > > 
> > > I do not understand why. I would be grateful if someone else
> > > can confirm the problem as well.
> > > 
> > > The commit's details are:
> > > 
> > > commit 66c1ca019078220dc1bf968f2bb18421100ef147
> > > Author: Andrea Righi <righi.andrea@...il.com>
> > > Date:   Tue Mar 31 15:25:18 2009 -0700
> > > 
> > >     fbmem: fix fb_info->lock and mm->mmap_sem circular locking dependency
> > 
> > Any lockdep info or oops? it just locks up the system?
> 
> # echo d > /proc/sysrq-trigger
> 
> [  187.654947] INFO: lockdep is turned off.
> 
> Strange, I do have lockdep enabled:
> 
> CONFIG_LOCKDEP_SUPPORT=y
> CONFIG_LOCKDEP=y
> CONFIG_DEBUG_LOCKDEP=y

Probably because lockdep reported the first lock bug and disabled the
checking for the next lock bugs, to avoid log flooding of follow-up
bugs. Search the first lockdep occurrence in dmesg.

-Andrea
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