Re: fix iounmap and a pageattr memleak (x86 and x86-64)

[Jason Baron <jbaron@redhat.com>]

On Tue, 2 Nov 2004, Dave Hansen wrote:

> This patch:
> 
> > From: Andrea Arcangeli <andrea@novell.com>
> > 
> > - fix silent memleak in the pageattr code that I found while searching
> >   for the bug Andi fixed in the second patch below (basically reference
> >   counting in split page was done on the pmd instead of the pte).
> > 
> > - Part of this patch is also needed to make the above work on x86 (otherwise
> >   one of my new above BUGS() will trigger signalling the fact a bug was
> >   there).  The below patch creates a subtle dependency that (_PAGE_PCD << 24)
> >   must not be zero.  It's not the cleanest thing ever, but since it's an
> >   hardware bitflag I doubt it's going to break.
> > 
> > Signed-off-by: Andi Kleen <ak@suse.de>
> > Signed-off-by: Andrea Arcangeli <andrea@novell.com>
> > Signed-off-by: Andrew Morton <akpm@osdl.org>
> > ---
> > 
> >  25-akpm/arch/i386/mm/ioremap.c    |    4 ++--
> >  25-akpm/arch/i386/mm/pageattr.c   |   13 +++++++------
> >  25-akpm/arch/x86_64/mm/ioremap.c  |   14 +++++++-------
> >  25-akpm/arch/x86_64/mm/pageattr.c |   23 ++++++++++++++---------
> >  4 files changed, 30 insertions(+), 24 deletions(-)
> 
> is hitting this BUG() during bootup:
> 
>         /* memleak and potential failed 2M page regeneration */
>         BUG_ON(!page_count(kpte_page));
> 
> in 2.6.10-rc1-mm2.
> 

I've seen the page_count being -1 (not sure why), for a number of pages in
the identity mapped region...So the BUG() on 0 doesn't seem valid to me.
 
Also, in order to tell if the pages should be merged back to create a huge
page, i don't see how the patch differentiates b/w pages that were split
and those that weren't simply based on the page_count....

-Jason



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