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

Rafael J. Wysocki
2008-11-15T11:47:20Z

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@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>

Thanks, closed.

Rafael