linux-kernel - Re: tty, vt: lockdep warnings

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Message-ID: <20121106164214.GA18246@redhat.com>
Date:	Tue, 6 Nov 2012 11:42:15 -0500
From:	Dave Jones <davej@...hat.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Hugh Dickins <hughd@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Sasha Levin <levinsasha928@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>, linux-kernel@...r.kernel.org,
	linux-fbdev@...r.kernel.org, florianSchandinat@....de
Subject: Re: tty, vt: lockdep warnings

On Tue, Nov 06, 2012 at 04:11:00PM +0000, Alan Cox wrote:

 > > But a deadlock we have lived with for years.  Without reverting,
 > > we're prevented from discovering all the new deadlocks we're adding.
 > 
 > We lived with it locking boxes up on users but not knowing why.

Circa 3.5 we got a lot more reports of this happening too for some reason.
Turns out that races are awfully resistant to bisecting too.

 > The root
 > cause is loading two different framebuffers with one taking over from
 > another - that should be an obscure corner case and once the fuzz testing
 > can avoid.
 > 
 > I had a semi-informed poke at this and came up with a possible patch (not very tested)

If this fixes the real problems we've been seeing, I'll dance a jig.
 
	Dave

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