linux-kernel - Re: [Bug #11988] Eliminate recursive mutex in compat fb ioctl path

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Date:	Sat, 15 Nov 2008 12:51:37 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Keith Packard <keithp@...thp.com>
Subject: Re: [Bug #11988] Eliminate recursive mutex in compat fb ioctl path

On Friday, 14 of November 2008, Geert Uytterhoeven wrote:
> On Sun, 9 Nov 2008, Rafael J. Wysocki wrote:
> > This message has been generated automatically as a part of a report
> > of recent regressions.
> > 
> > The following bug entry is on the current list of known regressions
> > from 2.6.27.  Please verify if it still should be listed and let me know
> > (either way).
> > 
> > 
> > Bug-Entry	: http://bugzilla.kernel.org/show_bug.cgi?id=11988
> > Subject		: Eliminate recursive mutex in compat fb ioctl path
> > Submitter	: Keith Packard <keithp@...thp.com>
> > Date		: 2008-11-03 7:06 (7 days old)
> > References	: http://marc.info/?l=linux-kernel&m=122569604828448&w=4
> > Handled-By	: Keith Packard <keithp@...thp.com>
> > 		  Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>
> > Patch		: http://marc.info/?l=linux-kernel&m=122569604828448&w=4
> > 		  http://lkml.org/lkml/2008/10/31/162
> 
> Fixed in mainline.
> 
> commit a684e7d33096892093456dd56a582cfc3bfad648
> Author: Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>
> Date:   Thu Nov 6 12:53:37 2008 -0800
> 
>     fbdev: fix fb_compat_ioctl() deadlocks
> 
>     commit 3e680aae4e53ab54cdbb0c29257dae0cbb158e1c ("fb: convert
>     lock/unlock_kernel() into local fb mutex") introduced several deadlocks
>     in the fb_compat_ioctl() path, as mutex_lock() doesn't allow recursion,
>     unlike lock_kernel().  This broke frame buffer applications on 64-bit
>     systems with a 32-bit userland.
>     
>     commit 120a37470c2831fea49fdebaceb5a7039f700ce6 ("framebuffer compat_ioctl
>     deadlock") fixed one of the deadlocks.
>     
>     This patch fixes the remaining deadlocks:
>       - Revert commit 120a37470c2831fea49fdebaceb5a7039f700ce6,
>       - Extract the core logic of fb_ioctl() into a new function do_fb_ioctl(),
>       - Change all callsites of fb_ioctl() where info->lock is already held to
>         call do_fb_ioctl() instead,
>       - Add sparse annotations to all routines that take info->lock.
>     
>     Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>
>     Cc: Mikulas Patocka <mpatocka@...hat.com>
>     Cc: Krzysztof Helt <krzysztof.h1@...pl>
>     Cc: Alan Cox <alan@...rguk.ukuu.org.uk>
>     Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
>     Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>

Thanks, closed.

Rafael
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