Re: [PATCH v2 3/3] NFS: Fix a memory leak in nfs_readdir

From: Hugh Dickins <hughd@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Nick Piggin <npiggin@kernel.dk>,
	Nick Bowler <nbowler@elliptictech.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-nfs@vger.kernel.org, Rik van Riel <riel@redhat.com>,
	Christoph Hellwig <hch@lst.de>, Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH v2 3/3] NFS: Fix a memory leak in nfs_readdir
Date: Wed, 1 Dec 2010 13:02:48 -0800 (PST)	[thread overview]
Message-ID: <alpine.LSU.2.00.1012011258220.18662@tigran.mtv.corp.google.com> (raw)
In-Reply-To: <20101201123341.d12ef362.akpm@linux-foundation.org>

On Wed, 1 Dec 2010, Andrew Morton wrote:
> On Wed, 01 Dec 2010 15:10:50 -0500
> Trond Myklebust <Trond.Myklebust@netapp.com> wrote:
> 
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -602,6 +602,7 @@ struct address_space_operations {
> >  	sector_t (*bmap)(struct address_space *, sector_t);
> >  	void (*invalidatepage) (struct page *, unsigned long);
> >  	int (*releasepage) (struct page *, gfp_t);
> > +	void (*freepage)(struct page *);
> >  	ssize_t (*direct_IO)(int, struct kiocb *, const struct iovec *iov,
> >  			loff_t offset, unsigned long nr_segs);
> >  	int (*get_xip_mem)(struct address_space *, pgoff_t, int,
> 
> It would be good to think about and then clearly spell out exactly what
> state the page is in here.  It is locked, and I assume clean and not
> under writeback.  What about its refcount, freezedness status and
> eligibility for lookups?
> 
> And as Hugh pointed out, some callees might needs the address_space*
> although we can perhaps defer that until such a callee turns up. 
> If/when that happens we might have a problem though: if this locked
> page is no longer attached to the address_space then what now pins the
> address_space, protecting it from inode reclaim?

That's an excellent point and trumps mine: it would be actively wrong
to provide the struct address_space *mapping arg I was asking for.
(Bet someone then tries stashing it away via page->private though.)

Hugh