[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;