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

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Message-ID: <20101202100158.3387566c@notabene.brown>
Date:	Thu, 2 Dec 2010 10:01:58 +1100
From:	Neil Brown <neilb@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Trond Myklebust <Trond.Myklebust@...app.com>,
	Hugh Dickins <hughd@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Nick Bowler <nbowler@...iptictech.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-nfs@...r.kernel.org, Rik van Riel <riel@...hat.com>,
	Christoph Hellwig <hch@....de>,
	Al Viro <viro@...iv.linux.org.uk>,
	Nick Piggin <npiggin@...nel.dk>
Subject: Re: [PATCH v2 3/3] NFS: Fix a memory leak in nfs_readdir

On Wed, 1 Dec 2010 14:43:14 -0800 Andrew Morton <akpm@...ux-foundation.org>
wrote:

> On Thu, 2 Dec 2010 08:29:13 +1100
> Neil Brown <neilb@...e.de> wrote:
> 
> > > > 
> > > > However, while reading Documentation/filesystems/vfs.txt (in order to
> > > > add documentation for freepage) I was surprised to read that the
> > > > ->releasepage() is itself supposed to be allowed to actually remove the
> > > > page from the address space if it so desires.
> > > 
> > > That doesn't sound right.  It came from Neil in 2006.
> > > 
> > > Neil, what were you thinking there?   Did you find such a ->releasepage()?
> > 
> > Nope, no idea, sorry.
> > 
> > No releasepage functions do anything like that, and no call sites suggest it
> > could be a possibility.  Quite the reverse - they are likely to remove the
> > page from the mapping without checking that it is still in the mapping.
> > 
> > So that sentence should be deleted.
> 
> This?

Perfect, thanks.

NeilBrown


> 
> From: Andrew Morton <akpm@...ux-foundation.org>
> 
> ->releasepage() does not remove the page from the mapping.
> 
> Cc: Neil Brown <neilb@...e.de>
> Cc: Trond Myklebust <Trond.Myklebust@...app.com>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> ---
> 
>  Documentation/filesystems/vfs.txt |    9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff -puN Documentation/filesystems/vfs.txt~documentation-filesystems-vfstxt-fix-repeasepage-description Documentation/filesystems/vfs.txt
> --- a/Documentation/filesystems/vfs.txt~documentation-filesystems-vfstxt-fix-repeasepage-description
> +++ a/Documentation/filesystems/vfs.txt
> @@ -660,11 +660,10 @@ struct address_space_operations {
>    releasepage: releasepage is called on PagePrivate pages to indicate
>          that the page should be freed if possible.  ->releasepage
>          should remove any private data from the page and clear the
> -        PagePrivate flag.  It may also remove the page from the
> -        address_space.  If this fails for some reason, it may indicate
> -        failure with a 0 return value.
> -	This is used in two distinct though related cases.  The first
> -        is when the VM finds a clean page with no active users and
> +        PagePrivate flag. If releasepage() fails for some reason, it must
> +	indicate failure with a 0 return value.
> +	releasepage() is used in two distinct though related cases.  The
> +	first is when the VM finds a clean page with no active users and
>          wants to make it a free page.  If ->releasepage succeeds, the
>          page will be removed from the address_space and become free.
>  
> _

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