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

From: Rik van Riel
Date: Tue Apr 06 2010 - 10:36:25 EST

On 04/06/2010 06:09 AM, KOSAKI Motohiro wrote:
(b) is also impossible. SLAB_DESTROY_BY_RCU delay the page for anon_vma
freeing until next rcu period. It mean rcu_read_lock()+page_mapped()
can see kfree()ed page. but it is safe. noone corrupt it.

by the way: I haven't understand why rik's per process anon_vma concept
works correctly with ksm. ksm increase anon_vma->ksm_refcount. but it seems
not guranteed vma->anon_vma and page->anon_vma are the same.

KSM removes the page from its original anon_vma.

If the page gets reinstantiated (copy on write), it will be
created in the vma->anon_vma.

Am I overlooking something?
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