[PATCH V2] fbcon -- fix race between open and removal of framebuffers

[Tim Gardner]

This is a multi-part message in MIME format.On 05/05/2011 11:00 PM, Jack Stone wrote:
> On 05/05/2011 18:41, tim.gardner@xxxxxxxxxxxxx wrote:
> > +static struct fb_info *get_framebuffer_info(int idx)
> > +__acquires(&registered_lock)
> > +__releases(&registered_lock)
> > +{
> > +	struct fb_info *fb_info;
> > +
> > +	spin_lock(&registered_lock);
> > +	fb_info = registered_fb[idx];
> > +	fb_info->ref_count++;
> > +	spin_unlock(&registered_lock);
> > +
> > +	return fb_info;
> > +}
> > +
> >   static int
> >   fb_open(struct inode *inode, struct file *file)
> >   __acquires(&info->lock)
> > @@ -1363,13 +1421,17 @@ __releases(&info->lock)
> >
> >   	if (fbidx>= FB_MAX)
> >   		return -ENODEV;
> > -	info = registered_fb[fbidx];
> > +	info = get_framebuffer_info(fbidx);
> >   	if (!info)
> >   		request_module("fb%d", fbidx);
> > -	info = registered_fb[fbidx];
> > +	info = get_framebuffer_info(fbidx);
> >   	if (!info)
> >   		return -ENODEV;
>
> If the first get_framebuffer_info succeeds don't you up the ref count
> twice? Shouldn't this be:
>
> info = get_framebuffer_info(fbidx);
> if (!info) {
> 	request_module("fb%d", fbidx);
> 	info = get_framebuffer_info(fbidx);
> }
> if (!info)
> 	return -ENODEV;
>
> Thanks,
>
> Jack

Good catch. See attached.

rtg
--
Tim Gardner tim.gardner@xxxxxxxxxxxxx