[PATCH] Video: fb, add true ref_count atomicity

Some of fb drivers uses atomic_t in bad manner, since there are still some
race-prone gaps.  Use mutexes to protect open/close code sections with
ref_count testing and finally use simple uint.

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Acked-by: Denis Oliver Kropp <dok@directfb.org>
Cc: James Simmons <jsimmons@infradead.org>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 17 insertions, 11 deletions

diff --git a/drivers/video/i810/i810.h b/drivers/video/i810/i810.h
index 579195c2bea3..aa65ffce915b 100644
--- a/drivers/video/i810/i810.h
+++ b/drivers/video/i810/i810.h
@@ -264,7 +264,8 @@ struct i810fb_par {
         struct heap_data         cursor_heap;
         struct vgastate          state;
         struct i810fb_i2c_chan   chan[3];
-        atomic_t                 use_count;
+        struct mutex             open_lock;
+        unsigned int             use_count;
         u32 pseudo_palette[17];
         unsigned long mmio_start_phys;
         u8 __iomem *mmio_start_virtual;
diff --git a/drivers/video/i810/i810_main.c b/drivers/video/i810/i810_main.c
index b55a12d95eb2..e343c0da9618 100644
--- a/drivers/video/i810/i810_main.c
+++ b/drivers/video/i810/i810_main.c
@@ -1235,9 +1235,9 @@ static int i810fb_getcolreg(u8 regno, u8 *red, u8 *green, u8 *blue,
 static int i810fb_open(struct fb_info *info, int user)
 {
         struct i810fb_par *par = info->par;
-        u32 count = atomic_read(&par->use_count);
-        
-        if (count == 0) {
+
+        mutex_lock(&par->open_lock);
+        if (par->use_count == 0) {
                 memset(&par->state, 0, sizeof(struct vgastate));
                 par->state.flags = VGA_SAVE_CMAP;
                 par->state.vgabase = par->mmio_start_virtual;
@@ -1246,7 +1246,8 @@ static int i810fb_open(struct fb_info *info, int user)
                 i810_save_vga_state(par);
         }
 
-        atomic_inc(&par->use_count);
+        par->use_count++;
+        mutex_unlock(&par->open_lock);
         
         return 0;
 }
@@ -1254,18 +1255,20 @@ static int i810fb_open(struct fb_info *info, int user)
 static int i810fb_release(struct fb_info *info, int user)
 {
         struct i810fb_par *par = info->par;
-        u32 count;
-        
-        count = atomic_read(&par->use_count);
-        if (count == 0)
+
+        mutex_lock(&par->open_lock);
+        if (par->use_count == 0) {
+                mutex_unlock(&par->open_lock);
                 return -EINVAL;
+        }
 
-        if (count == 1) {
+        if (par->use_count == 1) {
                 i810_restore_vga_state(par);
                 restore_vga(&par->state);
         }
 
-        atomic_dec(&par->use_count);
+        par->use_count--;
+        mutex_unlock(&par->open_lock);
         
         return 0;
 }
@@ -1752,6 +1755,8 @@ static void __devinit i810_init_monspecs(struct fb_info *info)
 static void __devinit i810_init_defaults(struct i810fb_par *par, 
                                       struct fb_info *info)
 {
+        mutex_init(&par->open_lock);
+
         if (voffset) 
                 v_offset_default = voffset;
         else if (par->aperture.size > 32 * 1024 * 1024)