linux-kernel - Re: [patch] ksm: check for ERR_PTR from follow

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Message-ID: <20100421211052.GE5336@cmpxchg.org>
Date:	Wed, 21 Apr 2010 23:10:52 +0200
From:	Johannes Weiner <hannes@...xchg.org>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	Rik van Riel <riel@...hat.com>, Dan Carpenter <error27@...il.com>,
	Izik Eidus <ieidus@...hat.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	kernel-janitors@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [patch] ksm: check for ERR_PTR from follow_page()

On Wed, Apr 21, 2010 at 10:58:07PM +0200, Andrea Arcangeli wrote:
> On Wed, Apr 21, 2010 at 10:53:05PM +0200, Johannes Weiner wrote:
> > + * Returns the mapped (struct page *), %NULL if no mapping exists, or
> > + * an error pointer if there is a mapping to something not represented
> > + * by a page descriptor (see also vm_normal_page()).
> 
> where exactly in vm_normal_page? Note I already checked vm_normal_page
> before sending the prev email and I didn't immediately see.  I search
> return and they all return NULL except the return pfn_to_page(pfn), so
> is pfn_to_page that returns -EFAULT (the implementations I checked
> don't but there are plenty that I didn't check...).

It's not vm_normal_page() that returns -EFAULT.  It is follow_page()
that translates NULL from vm_normal_page() into -EFAULT.
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