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, 9 insertions, 5 deletions

diff --git a/drivers/video/fsl-diu-fb.c b/drivers/video/fsl-diu-fb.c
index f153c581cbd..0bf2190928d 100644
--- a/drivers/video/fsl-diu-fb.c
+++ b/drivers/video/fsl-diu-fb.c
@@ -750,24 +750,26 @@ static void update_lcdc(struct fb_info *info)
 static int map_video_memory(struct fb_info *info)
 {
 	phys_addr_t phys;
+	u32 smem_len = info->fix.line_length * info->var.yres_virtual;
 
 	pr_debug("info->var.xres_virtual = %d\n", info->var.xres_virtual);
 	pr_debug("info->var.yres_virtual = %d\n", info->var.yres_virtual);
 	pr_debug("info->fix.line_length  = %d\n", info->fix.line_length);
+	pr_debug("MAP_VIDEO_MEMORY: smem_len = %u\n", smem_len);
 
-	info->fix.smem_len = info->fix.line_length * info->var.yres_virtual;
-	pr_debug("MAP_VIDEO_MEMORY: smem_len = %d\n", info->fix.smem_len);
-	info->screen_base = fsl_diu_alloc(info->fix.smem_len, &phys);
+	info->screen_base = fsl_diu_alloc(smem_len, &phys);
 	if (info->screen_base == NULL) {
 		printk(KERN_ERR "Unable to allocate fb memory\n");
 		return -ENOMEM;
 	}
+	mutex_lock(&info->mm_lock);
 	info->fix.smem_start = (unsigned long) phys;
+	info->fix.smem_len = smem_len;
+	mutex_unlock(&info->mm_lock);
 	info->screen_size = info->fix.smem_len;
 
 	pr_debug("Allocated fb @ paddr=0x%08lx, size=%d.\n",
-				info->fix.smem_start,
-		info->fix.smem_len);
+		 info->fix.smem_start, info->fix.smem_len);
 	pr_debug("screen base %p\n", info->screen_base);
 
 	return 0;
@@ -776,9 +778,11 @@ static int map_video_memory(struct fb_info *info)
 static void unmap_video_memory(struct fb_info *info)
 {
 	fsl_diu_free(info->screen_base, info->fix.smem_len);
+	mutex_lock(&info->mm_lock);
 	info->screen_base = NULL;
 	info->fix.smem_start = 0;
 	info->fix.smem_len = 0;
+	mutex_unlock(&info->mm_lock);
 }
 
 /*