fbdev: Use device_create_with_groups() to fix sysfs groups registration race

The fbdev sysfs attributes are registered after sending the uevent for
the device creation, leaving a race window where e.g. udev rules may
not be able to access the sysfs attributes because the registration is
not done yet.

Fix this by switching to device_create_with_groups(). This also results in
a nice cleanup. After switching to device_create_with_groups() all that
is left of fb_init_device() is setting the drvdata and that can be passed
to device_create[_with_groups]() too. After which fb_init_device() can
be completely removed.

Dropping fb_init_device() + fb_cleanup_device() in turn allows removing
fb_info.class_flag as they were the only user of this field.

Fixes: 5fc830d ("fbdev: Register sysfs groups through device_add_group")
Cc: stable@vger.kernel.org
Cc: Shixiong Ou <oushixiong@kylinos.cn>
Signed-off-by: Hans de Goede <johannes.goede@oss.qualcomm.com>
Signed-off-by: Helge Deller <deller@gmx.de>

Author: Hans de Goede

drivers/video/fbdev/core/fbsysfs.c

@@ -12,8 +12,6 @@
 
 #include "fb_internal.h"
 
-#define FB_SYSFS_FLAG_ATTR 1
-
 static int activate(struct fb_info *fb_info, struct fb_var_screeninfo *var)
 {
 	int err;
@@ -451,48 +449,21 @@ static struct attribute *fb_device_attrs[] = {
 	NULL,
 };
 
-static const struct attribute_group fb_device_attr_group = {
-	.attrs          = fb_device_attrs,
-};
-
-static int fb_init_device(struct fb_info *fb_info)
-{
-	int ret;
-
-	dev_set_drvdata(fb_info->dev, fb_info);
-
-	fb_info->class_flag |= FB_SYSFS_FLAG_ATTR;
-
-	ret = device_add_group(fb_info->dev, &fb_device_attr_group);
-	if (ret)
-		fb_info->class_flag &= ~FB_SYSFS_FLAG_ATTR;
-
-	return 0;
-}
-
-static void fb_cleanup_device(struct fb_info *fb_info)
-{
-	if (fb_info->class_flag & FB_SYSFS_FLAG_ATTR) {
-		device_remove_group(fb_info->dev, &fb_device_attr_group);
-
-		fb_info->class_flag &= ~FB_SYSFS_FLAG_ATTR;
-	}
-}
+ATTRIBUTE_GROUPS(fb_device);
 
 int fb_device_create(struct fb_info *fb_info)
 {
 	int node = fb_info->node;
 	dev_t devt = MKDEV(FB_MAJOR, node);
 	int ret;
 
-	fb_info->dev = device_create(fb_class, fb_info->device, devt, NULL, "fb%d", node);
+	fb_info->dev = device_create_with_groups(fb_class, fb_info->device, devt, fb_info,
+						 fb_device_groups, "fb%d", node);
 	if (IS_ERR(fb_info->dev)) {
 		/* Not fatal */
 		ret = PTR_ERR(fb_info->dev);
 		pr_warn("Unable to create device for framebuffer %d; error %d\n", node, ret);
 		fb_info->dev = NULL;
-	} else {
-		fb_init_device(fb_info);
 	}
 
 	return 0;
@@ -505,7 +476,6 @@ void fb_device_destroy(struct fb_info *fb_info)
 	if (!fb_info->dev)
 		return;
 
-	fb_cleanup_device(fb_info);
 	device_destroy(fb_class, devt);
 	fb_info->dev = NULL;
 }

include/linux/fb.h

@@ -493,7 +493,6 @@ struct fb_info {
 #if defined(CONFIG_FB_DEVICE)
 	struct device *dev;		/* This is this fb device */
 #endif
-	int class_flag;                    /* private sysfs flags */
 #ifdef CONFIG_FB_TILEBLITTING
 	struct fb_tile_ops *tileops;    /* Tile Blitting */
 #endif