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

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Message-ID: <4CF67BBE.8050303@panasas.com>
Date:	Wed, 01 Dec 2010 18:45:50 +0200
From:	Benny Halevy <bhalevy@...asas.com>
To:	Rik van Riel <riel@...hat.com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	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 2010-12-01 18:35, Rik van Riel wrote:
> On 12/01/2010 11:17 AM, Linus Torvalds wrote:
> 
>> So this is a TOTALLY UNTESTED trivial patch that just adds another
>> callback. Does this work? I dunno. But I get the feeling that instead
>> of having NFS work around the odd semantics that don't actually match
>> what NFS wants, introducing a new callback with much simpler semantics
>> would be simpler for everybody, and avoid the need for subtle code.
> 
> Surely somebody can have just looked up the page and
> gotten a reference count, right before your ->freepage
> call is invoked?
> 
> CPU A				CPU B
> 
> look up page
> grab refcount
> 				->freepage
> 
> use contents of page
> 
> Am I overlooking something obvious?
> 

The page is not cached any more at this point therefore
looking it up won't find it.

Benny
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