Re: build problems on architectures where FIXADDR_* stuff is not constant

[Andrew Morton <akpm@digeo.com>]

Andrew Morton <akpm@digeo.com> wrote:
>
> The new code in get_user_pages() is rather rude - it's returning a
> statically allocated VMA which isn't in the VMA tree - the caller (who
> holds mmap_sem()) could reasonably expect that the VMA can be located via
> find_vma(), or removed from the tree or whatever.  But it cannot.
> 
> I think it needs to be redone.  Either by stuffing a VMA into every
> process's mm which describes the fixmap area, or by failing
> get_user_pages() if the caller has passed in a non-NULL `vmas' and is
> requesting access to the fixmap area.

Or by lazily instantiating the fixmap VMA within get_user_pages().  So if
someone happens to want to access the fixmap, that's when the vma which
describes it gets stuffed into the tree.

That'd require that get_user_pages() be called under down_write(mmap_sem).