Re: Ugly rmap NULL ptr deref oopsie on hibernate (was Linux2.6.34-rc3)

From: Minchan Kim
Date: Tue Apr 06 2010 - 11:35:17 EST

On Tue, 2010-04-06 at 10:38 -0400, Rik van Riel wrote:
> On 04/06/2010 04:53 AM, KOSAKI Motohiro wrote:
> > Today, I've reviewed this patch carefully. but I haven't found any bug.
> > Also, I've runned stress workload with shrink_all_memory() today. but
> > I couldn't reproduce the issue. hmm.. (perhaps I'm no lucky guy.
> > I'm frequently fail to reproduce)
> >
> > I'll continue to work.
> My status with this bug is the same - I have gone through
> the code from all angles, but have not found any other bugs
> yet (except for that leak - which could leave invalid
> pointers behind).

Let's see the unlink_anon_vmas.

1. list_for_each_entry_safe(avc,next, vma->anon_vma_chain, same_vma)
2. anon_vma_unlink
3. spin_lock(anon_vma->lock) <-- HERE LOCK.
4. list_del(anon_vma_chain->same_anon_vma);

What if anon_vma is destroyed and reuse by SLAB_XXX_RCU for another
anon_vma object between 2 and 3?
I mean how to make sure 3) does lock valid anon_vma?

I hope it is culprit.

Kind regards,
Minchan Kim

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