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, 2 insertions, 0 deletions

diff --git a/drivers/video/pxafb.c b/drivers/video/pxafb.c
index 0889d50c3288..6506117c134b 100644
--- a/drivers/video/pxafb.c
+++ b/drivers/video/pxafb.c
@@ -815,8 +815,10 @@ static int overlayfb_map_video_memory(struct pxafb_layer *ofb)
         ofb->video_mem_phys = virt_to_phys(ofb->video_mem);
         ofb->video_mem_size = size;
 
+        mutex_lock(&ofb->fb.mm_lock);
         ofb->fb.fix.smem_start  = ofb->video_mem_phys;
         ofb->fb.fix.smem_len    = ofb->fb.fix.line_length * var->yres_virtual;
+        mutex_unlock(&ofb->fb.mm_lock);
         ofb->fb.screen_base     = ofb->video_mem;
         return 0;
 }