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

From: Linus Torvalds
Date: Tue Apr 06 2010 - 12:33:20 EST

On Wed, 7 Apr 2010, Minchan Kim wrote:
> >
> > However, that made me look at the PAGE_MIGRATION case. That seems to be
> > just broken. It's doing that page_anon_vma() + spin_lock without holding
> > any RCU locks, so there is no guarantee that anon_vma there is at all
> > valid.
> FYI, recently there is a patch about migration case.

No, I'm talking about rmap_walk_anon():

anon_vma = page_anon_vma(page);
if (!anon_vma)
return ret;

which seems to be simply buggy. The anon_vma may not exist any more,
because an RCU event might have really freed the page between looking it
up and locking it.

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