linux-kernel - Re: mm: kernel BUG at mm/huge

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <532369AF.8020406@oracle.com>
Date:	Fri, 14 Mar 2014 16:42:23 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
CC:	Bob Liu <lliubbo@...il.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: mm: kernel BUG at mm/huge_memory.c:2785!

On 03/07/2014 07:18 AM, Kirill A. Shutemov wrote:
> On Thu, Mar 06, 2014 at 08:32:48PM -0500, Sasha Levin wrote:
>> On 03/04/2014 10:53 PM, Sasha Levin wrote:
>>> On 03/04/2014 10:16 PM, Bob Liu wrote:
>>>> On Thu, Feb 27, 2014 at 11:03 PM, Kirill A. Shutemov
>>>> <kirill.shutemov@...ux.intel.com> wrote:
>>>>> Sasha Levin wrote:
>>>>>> Hi all,
>>>>>>
>>>>>> While fuzzing with trinity inside a KVM tools guest running latest -next kernel I've stumbled on the
>>>>>> following spew:
>>>>>>
>>>>>> [ 1428.146261] kernel BUG at mm/huge_memory.c:2785!
>>>>>
>>>>> Hm, interesting.
>>>>>
>>>>> It seems we either failed to split huge page on vma split or it
>>>>> materialized from under us. I don't see how it can happen:
>>>>>
>>>>>    - it seems we do the right thing with vma_adjust_trans_huge() in
>>>>>      __split_vma();
>>>>>    - we hold ->mmap_sem all the way from vm_munmap(). At least I don't see
>>>>>      a place where we could drop it;
>>>>>
>>>>
>>>> Enable CONFIG_DEBUG_VM may show some useful information, at least we
>>>> can confirm weather rwsem_is_locked(&tlb->mm->mmap_sem) before
>>>> split_huge_page_pmd().
>>>
>>> I have CONFIG_DEBUG_VM enabled and that code you're talking is not triggering, so mmap_sem
>>> is locked.
>>
>> Guess what. I've just hit it.
>
> I think this particular traceback is not a real problem: by time of
> exit_mm() we shouldn't race with anybody for the mm_struct.
>
> We probably could drop ->mmap_sem later in mmput() rather then in
> exit_mm() to fix this false positive.
>
>> It's worth keeping in mind that this is the first time I see it.
>
> Hm. That's strange exit_mmap() is called without holding ->mmap_sem.
>

This issues does happen quite often and is very easy to reproduce, I could try
anything you can thing of.


Thanks,
Sasha
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/