linux-kernel - Re: [REGRESSION] commit 66c1ca0: {fbmem: fix fb_info->lock and mm->mmap

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Message-ID: <20090411193226.GA5440@linux>
Date:	Sat, 11 Apr 2009 21:32:26 +0200
From:	Andrea Righi <righi.andrea@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Stefan Richter <stefanr@...6.in-berlin.de>,
	Krzysztof Helt <krzysztof.h1@...zta.fm>,
	Eric Miao <eric.y.miao@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Andrey Borzenkov <arvidjaar@...il.com>,
	"Antonino A. Daplas" <adaplas@...il.com>,
	linux-fbdev-devel@...ts.sourceforge.net,
	linux-pm@...ts.linux-foundation.org, Dave Jones <davej@...hat.com>,
	Harvey Harrison <harvey.harrison@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Pavel Roskin <proski@....org>
Subject: Re: [REGRESSION] commit 66c1ca0: {fbmem: fix fb_info->lock and
	mm->mmap_sem ...} causes Xfbdev not working

On Sat, Apr 11, 2009 at 11:21:31AM -0700, Andrew Morton wrote:
> On Sat, 11 Apr 2009 17:04:00 +0200 Andrea Righi <righi.andrea@...il.com> wrote:
> 
> > fbdev: fix info->lock deadlock in fbcon_event_notify()
> > 
> > fb_notifier_call_chain() is called with info->lock held, i.e. in
> > do_fb_ioctl() => FBIOPUT_VSCREENINFO => fb_set_var() and the some
> > notifier callbacks, like fbcon_event_notify(), try to re-acquire
> > info->lock again.
> > 
> > Remove the lock/unlock_fb_info() in all the framebuffer notifier
> > callbacks' and be sure to always call fb_notifier_call_chain() with
> > info->lock held.
> 
> Thanks.  So do you think we should proceed with this patch instead of
> reverting 66c1ca0?

Yes, there's no need to revert 66c1ca0 now, otherwise we'll simply
reintroduce the info->lock / mm->mmap_sem circular locking dependency.

I'd like to test the fbdev mode switching, but it seems intelfb doesn't
support it with LVDS ports (and at the moment I've not a CRT here...).

Anyway, if someone will have troubles with mode switching I'm quite sure
we can fix it on top of this patch.

-Andrea
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