fput under mmap_sem

[Christoph Hellwig]

On Mon, Mar 16, 2009 at 09:19:21AM +1100, Dave Chinner wrote:
> This is a VM problem where it calls fput() with the mmap_sem() held
> in remove_vma(). It makes the incorrect assumption that filesystems
> will never use the same lock in the IO path and the inode release path.
> 
> This can deadlock if you are really unlucky.

I really wonder why other filesystems haven't hit this yet.  Any chance
we can get the fput moved out of mmap_sem to get rid of this class of
problems?