[RFC] fbmem: reset file->private_data on failed fb_open()

[Wu Fengguang]

I wrote this when looking at NULL dereference bug
https://bugzilla.kernel.org/show_bug.cgi?id=18912

Will it help by clearing private_data? I have no idea at all, because
for regular files, ->release won't be called on failed ->open. Just in
case there are some exceptions in fbmem...

---
 drivers/video/fbmem.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- linux-next.orig/drivers/video/fbmem.c	2011-06-09 10:36:06.000000000 +0800
+++ linux-next/drivers/video/fbmem.c	2011-06-09 10:39:30.000000000 +0800
@@ -1424,26 +1424,28 @@ __releases(&info->lock)
 	file->private_data = info;
 	if (info->fbops->fb_open) {
 		res = info->fbops->fb_open(info,1);
 		if (res)
 			module_put(info->fbops->owner);
 	}
 #ifdef CONFIG_FB_DEFERRED_IO
 	if (info->fbdefio)
 		fb_deferred_io_open(info, inode, file);
 #endif
 out:
 	mutex_unlock(&info->lock);
-	if (res)
+	if (res) {
+		file->private_data = NULL;
 		put_fb_info(info);
+	}
 	return res;
 }
 
 static int 
 fb_release(struct inode *inode, struct file *file)
 __acquires(&info->lock)
 __releases(&info->lock)
 {
 	struct fb_info * const info = file->private_data;
 
 	mutex_lock(&info->lock);
 	if (info->fbops->fb_release)
--
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