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

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Date:	Tue, 6 Apr 2010 09:53:57 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Minchan Kim <minchan.kim@...il.com>
cc:	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Borislav Petkov <bp@...en8.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lee Schermerhorn <Lee.Schermerhorn@...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)



On Wed, 7 Apr 2010, Minchan Kim wrote:
> 
> unmap_and_move
> 	remove_migration_ptes
> 		rmap_walk
> 			rmap_walk_anon
> 
> We always has rcu_read_lock about anon page in unmap_and_move.
> So I think it's not buggy. What am I missing?

Ok, in that case it's fine.

However, it does bring back my comment about all those anonvma changes: 
the locking is totally undocumented. 

Why isn't there a thing _saying_ that it's ok because of this?

Why is there no comment about the locking of that 'same_vma' / 
'vma->anon_vma_chain' except for the totally nonsensical one about 
page_table_lock (which doesn't protect _any_ of the other cases)?

		Linus
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