Re: [PATCH] mm: Downgrade mmap_sem before locking or populating onmmap

[Al Viro]

On Fri, Dec 14, 2012 at 03:14:50AM -0800, Andy Lutomirski wrote:

> > Wait a minute.  get_user_pages() relies on ->mmap_sem being held.  Unless
> > I'm seriously misreading your patch it removes that protection.  And yes,
> > I'm aware of execve-related exception; it's in special circumstances -
> > bprm->mm is guaranteed to be not shared (and we need to rearchitect that
> > area anyway, but that's a separate story).
> 
> Unless I completely screwed up the patch, ->mmap_sem is still held for
> read (it's downgraded from write).  It's just not held for write
> anymore.

Huh?  I'm talking about the call of get_user_pages() in aio_setup_ring().
With your patch it's done completely outside of ->mmap_sem, isn't it?
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