[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 <[e-mail]>
Acked-by: Denis Oliver Kropp <[e-mail]>
Cc: James Simmons <[e-mail]>
Cc: "Antonino A. Daplas" <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/video/i810/i810.h

···
 	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;

drivers/video/i810/i810_main.c

···
 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;
···
 		i810_save_vga_state(par);
 	}
 
-	atomic_inc(&par->use_count);
+	par->use_count++;
+	mutex_unlock(&par->open_lock);
 	
 	return 0;
 }
···
 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)
-		return -EINVAL;
 
-	if (count == 1) {
+	mutex_lock(&par->open_lock);
+	if (par->use_count == 0) {
+		mutex_unlock(&par->open_lock);
+		return -EINVAL;
+	}
+
+	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;
 }
···
 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)

drivers/video/neofb.c

···
 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;
 }
 
···
 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;
 }
 
···
 
 	info->fix.accel = id->driver_data;
 
+	mutex_init(&par->open_lock);
 	par->pci_burst = !nopciburst;
 	par->lcd_stretch = !nostretch;
 	par->libretto = libretto;

drivers/video/riva/fbdev.c

···
 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;
···
 	
 		riva_save_state(par, &par->initial_state);
 	}
-	atomic_inc(&par->ref_count);
+	par->ref_count++;
+	mutex_unlock(&par->open_lock);
 	NVTRACE_LEAVE();
 	return 0;
 }
···
 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);
···
 #endif
 		par->riva.LockUnlock(&par->riva, 1);
 	}
-	atomic_dec(&par->ref_count);
+	par->ref_count--;
+	mutex_unlock(&par->open_lock);
 	NVTRACE_LEAVE();
 	return 0;
 }
···
 		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;

drivers/video/riva/rivafb.h

···
 #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;

drivers/video/vga16fb.c

···
 		unsigned char	ClockingMode;	  /* Seq-Controller:01h */
 	} vga_state;
 	struct vgastate state;
-	atomic_t ref_count;
+	struct mutex open_lock;
+	unsigned int ref_count;
 	int palette_blanked, vesa_blanked, mode, isVGA;
 	u8 misc, pel_msk, vss, clkdiv;
 	u8 crtc[VGA_CRT_C];
···
 static int vga16fb_open(struct fb_info *info, int user)
 {
 	struct vga16fb_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_FONTS | VGA_SAVE_MODE |
 			VGA_SAVE_CMAP;
 		save_vga(&par->state);
 	}
-	atomic_inc(&par->ref_count);
+	par->ref_count++;
+	mutex_unlock(&par->open_lock);
+
 	return 0;
 }
 
 static int vga16fb_release(struct fb_info *info, int user)
 {
 	struct vga16fb_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;
 }
···
 	printk(KERN_INFO "vga16fb: mapped to 0x%p\n", info->screen_base);
 	par = info->par;
 
+	mutex_init(&par->open_lock);
 	par->isVGA = ORIG_VIDEO_ISVGA;
 	par->palette_blanked = 0;
 	par->vesa_blanked = 0;

include/video/neomagic.h

···
 
 struct neofb_par {
 	struct vgastate state;
-	atomic_t ref_count;
+	struct mutex open_lock;
+	unsigned int ref_count;
 
 	unsigned char MiscOutReg;	/* Misc */
 	unsigned char CRTC[25];		/* Crtc Controller */