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);
 }
 
 /*