linux-kernel - Re: [PATCH v2 3/3] NFS: Fix a memory leak in nfs

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Message-ID: <4CF67F8E.6050308@redhat.com>
Date:	Wed, 01 Dec 2010 12:02:06 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Trond Myklebust <Trond.Myklebust@...app.com>,
	Nick Bowler <nbowler@...iptictech.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-nfs@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Christoph Hellwig <hch@....de>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v2 3/3] NFS: Fix a memory leak in nfs_readdir

On 12/01/2010 11:47 AM, Linus Torvalds wrote:
> On Wed, Dec 1, 2010 at 8:35 AM, Rik van Riel<riel@...hat.com>  wrote:
>>
>> Surely somebody can have just looked up the page and
>> gotten a reference count, right before your ->freepage
>> call is invoked?
>
> No.
>
> The removal from the page cache is atomic, even in the presence of the
> lockless lookup.
>
> The page cache lookup does a "get_page_unless_zero()" on the count, so
> when __remove_mapping() has removed the page using
> "page_freeze_refs()", it's really gone, and cannot be looked up.

Doh, you're right.  I forgot to look at all the stuff that
__remove_mapping does nowadays and remembered some very old
code from vmscan.c instead.

Acked-by: Rik van Riel <riel@...hat.com>

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