linux-kernel - Re: memory leak in alloc_huge

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Date:	Tue, 1 Dec 2015 16:54:21 -0800
From:	Mike Kravetz <mike.kravetz@...cle.com>
To:	Dmitry Vyukov <dvyukov@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Hillf Danton <hillf.zj@...baba-inc.com>,
	David Rientjes <rientjes@...gle.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Hugh Dickins <hughd@...gle.com>,
	Greg Thelen <gthelen@...gle.com>,
	syzkaller <syzkaller@...glegroups.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: memory leak in alloc_huge_page

On 12/01/2015 11:45 AM, Dmitry Vyukov wrote:
> On Tue, Dec 1, 2015 at 7:52 PM, Mike Kravetz <mike.kravetz@...cle.com> wrote:
>> On 12/01/2015 06:04 AM, Dmitry Vyukov wrote:

>>> There seems to be another leak if nrg is not NULL on this path, but
>>> it's not what happens in my case since the WARNING does not fire.
>>
>> If nrg is not NULL, then it was added to the resv map and 'should' be
>> free'ed when the map is free'ed.  This is not optimal, but I do not
>> think it would lead to a leak.  I'll take a close look at this code
>> with an emphasis on the leak you discovered.
> 
> 
> Hi Mike,
> 
> Note that it's not just a leak report, it is an actual leak. You
> should be able to reproduce it.
> 

OK, finally found the bug which is in region_del().  It does not correctly
handle a "placeholder" region descriptor that is left after an aborted
operation when the start of the region to be deleted is for the same page.

I will have a patch shortly, after some testing.

-- 
Mike Kravetz
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