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

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Message-Id: <20100406190036.7E66.A69D9226@jp.fujitsu.com>
Date:	Tue,  6 Apr 2010 19:09:08 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>, Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Minchan Kim <minchan.kim@...il.com>,
	Nick Piggin <npiggin@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>
Subject: Re: Ugly rmap NULL ptr deref oopsie on hibernate (was Linux 2.6.34-rc3)

> (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.

but I guess bug reporter doesn't use ksm, it's minor feature.



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