Re: Ugly rmap NULL ptr deref oopsie on hibernate (was Linux 2.6.34-rc3)

From: Rik van Riel
Date: Tue Apr 06 2010 - 11:42:14 EST

On 04/06/2010 11:34 AM, Minchan Kim wrote:

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.

How can the anon_vma get destroyed and reused, when this
anon_vma_chain still has a reference to it (and the
anon_vma has not been freed yet)?

What combination of circumstances is necessary for
your bug hypothetical to happen?
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