Re: [Bug #12606] fb_mmap: circular locking dependency on hibernation

Andrea Righi
2009-02-08T22:05:52Z

On 2009-02-08 20:21, 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 2.6.28. Please verify if it still should be listed and let me know
> (either way).
>
>
> Bug-Entry : http://bugzilla.kernel.org/show_bug.cgi?id=12606
> Subject : fb_mmap: circular locking dependency on hibernation
> Submitter : Andrey Borzenkov <arvidjaar@mail.ru>
> Date : 2009-01-27 18:37 (13 days old)
> References : http://marc.info/?l=linux-kernel&m=123308162731408&w=4
> Handled-By : Andrea Righi <righi.andrea@gmail.com>
> Patch : http://marc.info/?l=linux-kernel&m=123365581406194&w=2

This is fixed by:

commit 1f5e31d7e55ac7fbd4ec5e5b20c8868b0e4564c9
Author: Andrea Righi <righi.andrea@gmail.com>
Date: Wed Feb 4 15:12:03 2009 -0800

fbmem: don't call copy_from/to_user() with mutex held

Avoid calling copy_from/to_user() with fb_info->lock mutex held in fbmem
ioctl().

fb_mmap() is called under mm->mmap_sem (A) held, that also acquires
fb_info->lock (B); fb_ioctl() takes fb_info->lock (B) and does
copy_from/to_user() that might acquire mm->mmap_sem (A), causing a
deadlock.

NOTE: it doesn't push down the fb_info->lock in each own driver's
fb_ioctl(), so there are still potential deadlocks elsewhere.

Signed-off-by: Andrea Righi <righi.andrea@gmail.com>
Cc: Dave Jones <davej@redhat.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Johannes Weiner <hannes@saeurebad.de>
Cc: Krzysztof Helt <krzysztof.h1@wp.pl>
Cc: Harvey Harrison <harvey.harrison@gmail.com>
Cc: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>