linux-kernel - Re: [lkp] [mm] 7d2eba0557: BUG: unable to handle kernel NULL pointer dereference at (null)

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Message-ID: <569EC1C2.1060906@suse.cz>
Date:	Wed, 20 Jan 2016 00:07:46 +0100
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Cyrill Gorcunov <gorcunov@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	kernel test robot <ying.huang@...ux.intel.com>,
	Ebru Akagunduz <ebru.akagunduz@...il.com>, lkp@...org,
	LKML <linux-kernel@...r.kernel.org>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Mel Gorman <mgorman@...e.de>, Xie XiuQi <xiexiuqi@...wei.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Rik van Riel <riel@...hat.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [lkp] [mm] 7d2eba0557: BUG: unable to handle kernel NULL pointer
 dereference at (null)

On 01/19/2016 11:45 PM, Cyrill Gorcunov wrote:
> On Tue, Jan 19, 2016 at 02:30:45PM -0800, David Rientjes wrote:
>> On Tue, 19 Jan 2016, Cyrill Gorcunov wrote:
>> 
>> > Seems it should be something like that (untested at moment, please
>> > take a look).
>> > ---
>> > From: Cyrill Gorcunov <gorcunov@...nvz.org>
>> > Subject: [PATCH] mm: Fix tracepoint for scanning pages
>> > 
>> > The page might be NULL so use page_to_pfn in conditional call.
>> > 
>> > Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org>
>> 
>> I think this is obviously correct, so
>> 
>> Acked-by: David Rientjes <rientjes@...gle.com>
> 
> Thank you. I've compile tested it, but didn't run.

This has been in mmotm since november:
http://ozlabs.org/~akpm/mmotm/broken-out/mm-fix-kernel-crash-in-khugepaged-thread.patch

Although your patch does use -1UL instead of -1 (AFAICS the only difference, but
it's too late here), which Steven Rostedt suggested, so it's probably better.