From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <stable-owner@vger.kernel.org>
Received: from imap1.codethink.co.uk ([176.9.8.82]:45449 "EHLO
        imap1.codethink.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1751255AbdLEQSB (ORCPT
        <rfc822;stable@vger.kernel.org>); Tue, 5 Dec 2017 11:18:01 -0500
Message-ID: <1512490673.18523.176.camel@codethink.co.uk>
Subject: Re: [PATCH stable-4.4 1/2] mm: check the return value of
 lookup_page_ext for all call sites
From: Ben Hutchings <ben.hutchings@codethink.co.uk>
To: Michal Hocko <mhocko@kernel.org>,
        Greg KH <gregkh@linuxfoundation.org>
Cc: jaewon31.kim@samsung.com, akpm@linux-foundation.org,
        js1304@gmail.com, mhocko@suse.com, minchan@kernel.org,
        stable@vger.kernel.org, torvalds@linux-foundation.org,
        Yang Shi <yang.shi@linaro.org>, Arnd Bergmann <arnd@arndb.de>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>
Date: Tue, 05 Dec 2017 16:17:53 +0000
In-Reply-To: <1512490595.18523.175.camel@codethink.co.uk>
References: <1511339877204@kroah.com>
         <20171122120937.14241-1-mhocko@kernel.org>
         <1512490595.18523.175.camel@codethink.co.uk>
Content-Type: text/plain; charset="UTF-8"
Mime-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: stable-owner@vger.kernel.org
List-ID: <stable.vger.kernel.org>

Sorry, I see this got fixed already.

Ben.

On Tue, 2017-12-05 at 16:16 +0000, Ben Hutchings wrote:
> On Wed, 2017-11-22 at 13:09 +0100, Michal Hocko wrote:
> > From: Yang Shi <yang.shi@linaro.org>
> > 
> > commit f86e4271978bd93db466d6a95dad4b0fdcdb04f6 upstream.
> > 
> > Per the discussion with Joonsoo Kim [1], we need check the return value
> > of lookup_page_ext() for all call sites since it might return NULL in
> > some cases, although it is unlikely, i.e.  memory hotplug.
> > 
> > Tested with ltp with "page_owner=0".
> 
> [...]
> > --- a/mm/debug-pagealloc.c
> > +++ b/mm/debug-pagealloc.c
> > @@ -34,6 +34,8 @@ static inline void set_page_poison(struct page
> > *page)
> >  	struct page_ext *page_ext;
> >  
> >  	page_ext = lookup_page_ext(page);
> > +	if (page_ext)
> > +		return;
> 
> This, and the other checks added to debug-pagealloc.c, are reversed. 
> (This is specific to the 4.4 backport - in the upstream version these
> functions are in mm/page_poison.c and were patched correctly.)
> 
> Ben.
> 
> >  	__set_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
> >  }
> >  
> > @@ -42,6 +44,8 @@ static inline void clear_page_poison(struct page
> > *page)
> >  	struct page_ext *page_ext;
> >  
> >  	page_ext = lookup_page_ext(page);
> > +	if (page_ext)
> > +		return;
> >  	__clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
> >  }
> >  
> > @@ -50,6 +54,8 @@ static inline bool page_poison(struct page *page)
> >  	struct page_ext *page_ext;
> >  
> >  	page_ext = lookup_page_ext(page);
> > +	if (page_ext)
> > +		return false;
> >  	return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
> >  }
> >  
> 
> [...]
> 
-- 
Ben Hutchings
Software Developer, Codethink Ltd.