Re: memory management issues

On Sun, 2007-05-06 at 09:23 -0500, James Bottomley wrote:
> On Thu, 2007-05-03 at 01:11 -0700, Ollie Wild wrote:
> > Is this a bug in get_user_pages()?  Should it be calling
> > flush_cache_page() directly?
> 
> Just for the sake of completeness, the answer to this is "no".  The
> anonymous page part of get_user_pages() is designed to gather pages from
> current processes only (an then, the only in-tree user we have is fuse
> and that's a bit of a hack).  The problem with your patch is that you're
> trying to gather non-current pages.
> 
> It took me a while to discover this, largely because you do this:
> 
> +                               ret = get_user_pages(current, bprm->mm, pos,
> +                                                    1, 1, 1, &page, NULL);
> 
> That's horribly wrong ... you can't use the current process context to
> gather non-current pages ... if anything goes wrong and the page needs
> faulting (unusual for a nascent process, but not impossible) you'll get
> into terrible trouble because the mapping for the page isn't in current.

Right, what would be the proper way to go about this, a NULL tsk?
Because the bprm->mm is un-owned at this point in time. That is, there
is no process context associated with it at all.