linux-kernel - Re: [PATCH] fb: Rework locking to fix lock ordering on takeover

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Message-ID: <20121121125310.00625f55@pyramind.ukuu.org.uk>
Date:	Wed, 21 Nov 2012 12:53:10 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Josh Boyer <jwboyer@...il.com>
Cc:	linux-kernel@...r.kernel.org, florianschandinat@....de
Subject: Re: [PATCH] fb: Rework locking to fix lock ordering on takeover

On Wed, 21 Nov 2012 07:45:45 -0500
Josh Boyer <jwboyer@...il.com> wrote:

> On Fri, Nov 16, 2012 at 2:27 PM, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
> >
> > [The fb maintainer appears to be absent at the moment].
> >
> > This is needed to fix a pile of lockdep splats that now show up because console_lock()
> > is being properly audited. Hugh Dickins and Sasha Levin have tested it and both reports
> > all looks good. This is probably not the whole story - the entire fb layer has locking
> > confusion problems that were previously hidden but it seems to get the ones people hit
> > in testing. This hopefully explains a few of the weird fb hangs that have been floating
> > around forever.
> >
> > From: Alan Cox <alan@...ux.intel.com>
> >
> > Adjust the console layer to allow a take over call where the caller already
> > holds the locks. Make the fb layer lock in order.
> >
> > This s partly a band aid, the fb layer is terminally confused about the
> > locking rules it uses for its notifiers it seems.
> >
> > Signed-off-by: Alan Cox <alan@...ux.intel.com>
> 
> Should this eventually get into the stable trees?

Thats a question I'm not sure about at this point. I think the bug is
real but not caught by the lock checker in older trees but I've not
investigated.

Alan
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