linux-kernel - Re: [PATCH -v2] rmap: make anon_vma_prepare link in all the anon

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Message-Id: <20100413194443.D116.A69D9226@jp.fujitsu.com>
Date:	Tue, 13 Apr 2010 19:53:33 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	kosaki.motohiro@...fujitsu.com, Rik van Riel <riel@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan.kim@...il.com>,
	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>,
	sgunderson@...foot.com
Subject: Re: [PATCH -v2] rmap: make anon_vma_prepare link in all the anon_vmas of a mergeable VMA

>  struct anon_vma *page_lock_anon_vma(struct page *page)
>  {
> @@ -294,14 +309,24 @@ struct anon_vma *page_lock_anon_vma(struct page *page)
>  	unsigned long anon_mapping;
>  
>  	rcu_read_lock();
> -	anon_mapping = (unsigned long) ACCESS_ONCE(page->mapping);
> +	anon_mapping = (unsigned long)rcu_dereference(page->mapping);
>  	if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
>  		goto out;
> -	if (!page_mapped(page))
> -		goto out;
>  
>  	anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
>  	spin_lock(&anon_vma->lock);

Does anon->lock dereference is guranteed if page->_mapcount==-1?
It can be freed miliseconds ago, rcu_read_lock() doesn't provide such
gurantee.

perhaps, I'm missing your point.


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