From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrea Arcangeli <aarcange@redhat.com>
Date: Wed, 21 Apr 2010 20:58:07 +0000
Subject: Re: [patch] ksm: check for ERR_PTR from follow_page()
Message-Id: <20100421205807.GV32034@random.random>
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References: <20100421102759.GA29647@bicker>
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 <20100421174615.GO32034@random.random>
 <20100421205305.GO20640@cmpxchg.org>
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To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Rik van Riel <riel@redhat.com>, Dan Carpenter <error27@gmail.com>, Izik Eidus <ieidus@redhat.com>, Hugh Dickins <hugh.dickins@tiscali.co.uk>, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel-janitors@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>

On Wed, Apr 21, 2010 at 10:53:05PM +0200, Johannes Weiner wrote:
> Check below that loop.  If it returns non-null, the first check is
> whether it IS_ERR().

Indeed.

> + * 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...).