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

[Add CC to Thomas Creutz]

On Thu, Jun 09, 2011 at 02:10:19PM +0800, Bruno Prémont wrote:

On Thu, 9 Jun 2011 11:06:28 Wu Fengguang [off-list ref] wrote:

quoted

I wrote this when looking at NULL dereference bug
https://bugzilla.kernel.org/show_bug.cgi?id912

The trace over there rather looks like closing of a framebuffer that
has been replaced (and destroyed) during boot sequence.
This action happens when switching from VESA to KMS from initrd
or early userspace boot sequence where plymouthd had already opened
vesafb.

That should hopefully be fixed by refcounting FBs as done during
2.6.39-rc7.

That's great! Then hopefully the bug can be closed?

quoted

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...

fb devices files should be just as regular as any other device files...

Good, thanks for the confirmation.

Thanks,
Fengguang

quoted

---
 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)