[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>

1 files changed, 14 insertions, 7 deletions

diff --git a/drivers/video/neofb.c b/drivers/video/neofb.c
index 459ca553ffc0..395ccedde9a6 100644
--- a/drivers/video/neofb.c
+++ b/drivers/video/neofb.c
@@ -556,14 +556,16 @@ static int
 neofb_open(struct fb_info *info, int user)
 {
         struct neofb_par *par = info->par;
-        int cnt = atomic_read(&par->ref_count);
 
-        if (!cnt) {
+        mutex_lock(&par->open_lock);
+        if (!par->ref_count) {
                 memset(&par->state, 0, sizeof(struct vgastate));
                 par->state.flags = VGA_SAVE_MODE | VGA_SAVE_FONTS;
                 save_vga(&par->state);
         }
-        atomic_inc(&par->ref_count);
+        par->ref_count++;
+        mutex_unlock(&par->open_lock);
+
         return 0;
 }
 
@@ -571,14 +573,18 @@ static int
 neofb_release(struct fb_info *info, int user)
 {
         struct neofb_par *par = info->par;
-        int cnt = atomic_read(&par->ref_count);
 
-        if (!cnt)
+        mutex_lock(&par->open_lock);
+        if (!par->ref_count) {
+                mutex_unlock(&par->open_lock);
                 return -EINVAL;
-        if (cnt == 1) {
+        }
+        if (par->ref_count == 1) {
                 restore_vga(&par->state);
         }
-        atomic_dec(&par->ref_count);
+        par->ref_count--;
+        mutex_unlock(&par->open_lock);
+
         return 0;
 }
 
@@ -2047,6 +2053,7 @@ static struct fb_info *__devinit neo_alloc_fb_info(struct pci_dev *dev, const st
 
         info->fix.accel = id->driver_data;
 
+        mutex_init(&par->open_lock);
         par->pci_burst = !nopciburst;
         par->lcd_stretch = !nostretch;
         par->libretto = libretto;