fbdev: add mutex for fb_mmap locking

Add a mutex to avoid a circular locking problem between the mm layer
semaphore and fbdev ioctl mutex through the fb_mmap() call.

Also, add mutex to all places where smem_start and smem_len fields change
so the mutex inside the fb_mmap() is actually used.  Changing of these
fields before calling the framebuffer_register() are not mutexed.

This is 2.6.31 material.  It removes one lockdep (fb_mmap() and
register_framebuffer()) but there is still another one (fb_release() and
register_framebuffer()).  It also cleans up handling of the smem_start and
smem_len fields used by mutexed section of the fb_mmap().

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/fb.h b/include/linux/fb.h
index dd68358996b..f847df9e99b 100644
--- a/include/linux/fb.h
+++ b/include/linux/fb.h
@@ -819,6 +819,7 @@ struct fb_info {
         int node;
         int flags;
         struct mutex lock;              /* Lock for open/release/ioctl funcs */
+        struct mutex mm_lock;           /* Lock for fb_mmap and smem_* fields */
         struct fb_var_screeninfo var;   /* Current var */
         struct fb_fix_screeninfo fix;   /* Current fix */
         struct fb_monspecs monspecs;    /* Current Monitor specs */