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, 4 insertions, 0 deletions

diff --git a/drivers/video/omap/omapfb_main.c b/drivers/video/omap/omapfb_main.c
index 060d72fe57cb..4ea99bfc37b4 100644
--- a/drivers/video/omap/omapfb_main.c
+++ b/drivers/video/omap/omapfb_main.c
@@ -393,8 +393,10 @@ static void set_fb_fix(struct fb_info *fbi)
 
         rg = &plane->fbdev->mem_desc.region[plane->idx];
         fbi->screen_base        = rg->vaddr;
+        mutex_lock(&fbi->mm_lock);
         fix->smem_start         = rg->paddr;
         fix->smem_len           = rg->size;
+        mutex_unlock(&fbi->mm_lock);
 
         fix->type = FB_TYPE_PACKED_PIXELS;
         bpp = var->bits_per_pixel;
@@ -886,8 +888,10 @@ static int omapfb_setup_mem(struct fb_info *fbi, struct omapfb_mem_info *mi)
                                  * plane memory is dealloce'd, the other
                                  * screen parameters in var / fix are invalid.
                                  */
+                                mutex_lock(&fbi->mm_lock);
                                 fbi->fix.smem_start = 0;
                                 fbi->fix.smem_len = 0;
+                                mutex_unlock(&fbi->mm_lock);
                         }
                 }
         }