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

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Message-ID: <1291247776.6609.79.camel@heimdal.trondhjem.org>
Date:	Wed, 01 Dec 2010 18:56:16 -0500
From:	Trond Myklebust <Trond.Myklebust@...app.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Nick Piggin <npiggin@...nel.dk>,
	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>
Subject: Re: [PATCH v2 3/3] NFS: Fix a memory leak in nfs_readdir

On Wed, 2010-12-01 at 15:46 -0800, Andrew Morton wrote:
> On Wed, 01 Dec 2010 18:21:16 -0500
> Trond Myklebust <Trond.Myklebust@...app.com> wrote:
> 
> > --- a/mm/truncate.c
> > +++ b/mm/truncate.c
> > @@ -108,6 +108,10 @@ truncate_complete_page(struct address_space *mapping, struct page *page)
> >  	clear_page_mlock(page);
> >  	remove_from_page_cache(page);
> >  	ClearPageMappedToDisk(page);
> > +
> > +	if (mapping->a_ops->freepage)
> > +		mapping->a_ops->freepage(page);
> > +
> >  	page_cache_release(page);	/* pagecache ref */
> >  	return 0;
> >  }
> 
> So here we're assuming that `mapping' was pinned by other means.
> 
> Fair enough, although subtle.  Even drop_pagecache_sb() got it right ;)
> 
> > @@ -390,6 +394,10 @@ invalidate_complete_page2(struct address_space *mapping, struct page *page)
> >  	__remove_from_page_cache(page);
> >  	spin_unlock_irq(&mapping->tree_lock);
> >  	mem_cgroup_uncharge_cache_page(page);
> > +
> > +	if (mapping->a_ops->freepage)
> > +		mapping->a_ops->freepage(page);
> > +
> >  	page_cache_release(page);	/* pagecache ref */
> >  	return 1;
> >  failed:
> 
> And here.

Yes. Both these functions are static, and their callers are assuming
that something is already pinning the underlying inode, so the above
should be quite safe.

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@...app.com
www.netapp.com

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