Date: Tue, 30 Mar 2004 00:50:57 +0200
From: Andrea Arcangeli <andrea@suse.de>
To: Rajesh Venkatasubramanian <vrajesh@umich.edu>
Cc: Hugh Dickins <hugh@veritas.com>, akpm@osdl.org,
       linux-kernel@vger.kernel.org
Subject: Re: 2.6.5-rc2-aa5
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On Mon, Mar 29, 2004 at 04:30:51PM -0500, Rajesh Venkatasubramanian wrote:
> 
> Andrew Moroton <akpm@osld.org> wrote:
> >> Andrea Arcangeli <andrea@suse.de> wrote:
> >>
> >> Notably there is a BUG_ON(page->mapping) triggering in
> >> page_remove_rmap in the pagecache case. that could be ex-pagecache
> >> being
> >> removed from pagecache before all ptes have been zapped, infact the
> >> page_remove_rmap triggers in the vmtruncate path.
> >
> > Confused.  vmtruncate zaps the ptes before removing pages from
> > pagecache,
> > so I'd expect a non-null ->mapping in page_remove_rmap() is a very
> > common
> > thing.  truncate a file which someone has mmapped and it'll happen every
> > time, will it not?
> 
> Andrea missed a not (!) in the BUG_ON. It is BUG_ON(!page->mapping).

Yep sorry ;)

> 
> The race Andrea hit _may_ be the mremap vs. vmtruncate race I hit:
> 
> http://marc.theaimsgroup.com/?l=linux-mm&m=107720111303624
> 
> A first truncate that raced with mremap and left an orphaned pte.
> The following truncate tried to clear the orphaned pte, and reached
> page_remove_rmap with page->mapping == NULL.
> 
> Yes. It can happen in all 2.4 and 2.6 kernels.

ok fine, so my WARN_ON should work.

> Hugh has a better fix than mine for the mremap vs. truncate race
> in his anobjrmap 7/6 patch.
> 
> http://marc.theaimsgroup.com/?l=linux-kernel&m=107998825716363
> 
> With prio_tree we have to modify Hugh's fix, though.

Hugh are you interested to extract the fix against mainline? The
anobjrmap 7/6 is doing most of stuff I don't really need with anon-vma.
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