linux-kernel - Re: [PATCH -v2] rmap: make anon_vma_prepare link in all the anon

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Date:	Fri, 9 Apr 2010 12:32:30 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Borislav Petkov <bp@...en8.de>
cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Nick Piggin <npiggin@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	sgunderson@...foot.com, hannes@...xchg.org
Subject: Re: [PATCH -v2] rmap: make anon_vma_prepare link in all the anon_vmas
 of a mergeable VMA



On Fri, 9 Apr 2010, Borislav Petkov wrote:
> > 
> > So what I _think_ will happen is that you'll be able to re-create the 
> > problem that started this all.  But I'd like to verify that, just because 
> > I'm anal and I'd like these things to be tested independently.
> 
> Heh, that was easy. Third hibernate cycle is a charm^Wboom :)

Ok, good to know that I'm still tracking ok on the issue.

> > So assuming that the original problem happens again, if you can then apply 
> > Rik's patch, but add a
> > 
> > 	dst->anon_vma = src->anon_vma;
> > 
> > to just before the success case (the "return 0") in anon_vma_clone(), 
> > that would be good.
> 
> It looks like this way we mangle the anon_vma chains somehow. From
> what I can see and if I'm not mistaken, we save the anon_vmas alright
> but end up in what seems like an endless list_for_each_entry()
> loop having grabbed anon_vma->lock in page_lock_anon_vma() and we
> can't seem to yield it through page_unlock_anon_vma() at the end of
> page_referenced_anon() so it has to be that code in between iterating
> over each list entry...

Ok. So scratch Rik's patch. It doesn't work even with the anon_vma set up.

Rik? I think it's back to you. I'm not going to bother committing the 
change to the anon_vma locking unless you actually need the locking 
guarantees for anon_vma_prepare().

And I've got the feeling that the proper fix is in the vma_adjust() 
handling if your original idea was right.

Anybody?

We're at the point where I've already delayed -rc4 several days because 
it's pointless cutting it without fixing this. One option is to just say 
"f*ck it, we'll revert it all and try again later". But it feels so 
close..

		Linus
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