[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, 14 insertions, 8 deletions

diff --git a/drivers/video/riva/fbdev.c b/drivers/video/riva/fbdev.c
index 1a13966b7d5b..7c19b5c2a541 100644
--- a/drivers/video/riva/fbdev.c
+++ b/drivers/video/riva/fbdev.c
@@ -1101,10 +1101,10 @@ static int riva_get_cmap_len(const struct fb_var_screeninfo *var)
 static int rivafb_open(struct fb_info *info, int user)
 {
         struct riva_par *par = info->par;
-        int cnt = atomic_read(&par->ref_count);
 
         NVTRACE_ENTER();
-        if (!cnt) {
+        mutex_lock(&par->open_lock);
+        if (!par->ref_count) {
 #ifdef CONFIG_X86
                 memset(&par->state, 0, sizeof(struct vgastate));
                 par->state.flags = VGA_SAVE_MODE  | VGA_SAVE_FONTS;
@@ -1119,7 +1119,8 @@ static int rivafb_open(struct fb_info *info, int user)
         
                 riva_save_state(par, &par->initial_state);
         }
-        atomic_inc(&par->ref_count);
+        par->ref_count++;
+        mutex_unlock(&par->open_lock);
         NVTRACE_LEAVE();
         return 0;
 }
@@ -1127,12 +1128,14 @@ static int rivafb_open(struct fb_info *info, int user)
 static int rivafb_release(struct fb_info *info, int user)
 {
         struct riva_par *par = info->par;
-        int cnt = atomic_read(&par->ref_count);
 
         NVTRACE_ENTER();
-        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) {
                 par->riva.LockUnlock(&par->riva, 0);
                 par->riva.LoadStateExt(&par->riva, &par->initial_state.ext);
                 riva_load_state(par, &par->initial_state);
@@ -1141,7 +1144,8 @@ static int rivafb_release(struct fb_info *info, int user)
 #endif
                 par->riva.LockUnlock(&par->riva, 1);
         }
-        atomic_dec(&par->ref_count);
+        par->ref_count--;
+        mutex_unlock(&par->open_lock);
         NVTRACE_LEAVE();
         return 0;
 }
@@ -1999,6 +2003,7 @@ static int __devinit rivafb_probe(struct pci_dev *pd,
                 goto err_disable_device;
         }
 
+        mutex_init(&default_par->open_lock);
         default_par->riva.Architecture = riva_get_arch(pd);
 
         default_par->Chipset = (pd->vendor << 16) | pd->device;
diff --git a/drivers/video/riva/rivafb.h b/drivers/video/riva/rivafb.h
index 7fa13fc9c413..48ead6d72f24 100644
--- a/drivers/video/riva/rivafb.h
+++ b/drivers/video/riva/rivafb.h
@@ -53,7 +53,8 @@ struct riva_par {
 #ifdef CONFIG_X86
         struct vgastate state;
 #endif
-        atomic_t ref_count;
+        struct mutex open_lock;
+        unsigned int ref_count;
         unsigned char *EDID;
         unsigned int Chipset;
         int forceCRTC;