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/platinumfb.c b/drivers/video/platinumfb.c
index 03b3670130a0..bacfabd9ce16 100644
--- a/drivers/video/platinumfb.c
+++ b/drivers/video/platinumfb.c
@@ -141,7 +141,9 @@ static int platinumfb_set_par (struct fb_info *info)
                 offset = 0x10;
 
         info->screen_base = pinfo->frame_buffer + init->fb_offset + offset;
+        mutex_lock(&info->mm_lock);
         info->fix.smem_start = (pinfo->frame_buffer_phys) + init->fb_offset + offset;
+        mutex_unlock(&info->mm_lock);
         info->fix.visual = (pinfo->cmode == CMODE_8) ?
                 FB_VISUAL_PSEUDOCOLOR : FB_VISUAL_DIRECTCOLOR;
         info->fix.line_length = vmode_attrs[pinfo->vmode-1].hres * (1<<pinfo->cmode)