Re: [patch] updated inotify for 2.6.12-rc3.

[John McCutchan <ttb@tentacle.dhs.org>]

On Fri, 2005-04-22 at 09:56 +0100, Al Viro wrote:
> > +static int inotify_ignore(struct inotify_device *dev, s32 wd)
> > +{
> > +	struct inotify_watch *watch;
> > +	struct inode *inode;
> > +
> > +	down(&dev->sem);
> > +	watch = idr_find(&dev->idr, wd);
> > +	if (unlikely(!watch)) {
> > +		up(&dev->sem);
> > +		return -EINVAL;
> > +	}
> > +	get_inotify_watch(watch);
> > +	up(&dev->sem);
> > +
> > +	inode = watch->inode;
> > +	down(&inode->inotify_sem);
> > +	down(&dev->sem);
> > +	remove_watch(watch, dev);
> > +	up(&dev->sem);
> > +	up(&inode->inotify_sem);
> > +	put_inotify_watch(watch);
> > +
> > +	return 0;
> > +}
> 
> So what happens if
> 	* something is holding inotify_sem right now
> 	* ten threads call that on the same watch
> 	* all of them get to down(&inode->inotify_sem); and block there,
> having acquired ten references to the watch
> 	* after whatever had been holding ->inotify_sem in the first place
> releases it, they will one by one go through the rest of function.  And
> drop _20_ references to the watch.  9 of those - after we kfree() the
> watch...

In create_watch () we call get_inotify_watch (), which maps to the
put_inotify_watch() in remove_watch(). As far as I can tell the ref
counting is 1 for 1.


-- 
John McCutchan <ttb@tentacle.dhs.org>