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

Geert Uytterhoeven
2008-11-14T14:51:57Z

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@keithp.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@keithp.com>
> Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.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@sonycom.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@sonycom.com>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: Krzysztof Helt <krzysztof.h1@wp.pl>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

With kind regards,

Geert Uytterhoeven
Software Architect

Sony Techsoft Centre Europe
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