linux-kernel - Re: [PATCH 1/2] fb: Rework locking to fix lock ordering on takeover

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Date:	Wed, 23 Jan 2013 17:38:42 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	Daniel Vetter <daniel.vetter@...ll.ch>
Cc:	Dave Airlie <airlied@...il.com>,
	Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
	DRI Development <dri-devel@...ts.freedesktop.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-fbdev-devel@...ts.sourceforge.net,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Alan Cox <alan@...ux.intel.com>
Subject: Re: [PATCH 1/2] fb: Rework locking to fix lock ordering on takeover

At Wed, 23 Jan 2013 17:25:08 +0100,
Daniel Vetter wrote:
> 
> From: Alan Cox <alan@...rguk.ukuu.org.uk>
> 
> 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>
> [danvet: Tiny whitespace cleanup.]
> Reported-and-tested-by: Hugh Dickins <hughd@...gle.com>
> Reported-and-tested-by: Sasha Levin <levinsasha928@...il.com>
> References: https://lkml.org/lkml/2012/10/25/516
> Signed-off-by: Daniel Vetter <daniel.vetter@...ll.ch>

FYI, the latest patch of this is found in mm tree:
  http://ozlabs.org/~akpm/mmots/broken-out/fb-rework-locking-to-fix-lock-ordering-on-takeover.patch

Also I hit the same problem in another code paths (for unbind and
unregister):
  http://marc.info/?t=135309396400003&r=1&w=2

My additional patch is found in mm tree, too:
  http://ozlabs.org/~akpm/mmots/broken-out/fb-yet-another-band-aid-for-fixing-lockdep-mess.patch


Takashi
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