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

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Message-ID: <CAA_GA1c02iSmkmCLHFkrK4b4W+JppZ4CSMUJ-Wn1rCs-c=dV6g@mail.gmail.com>
Date:	Wed, 5 Mar 2014 11:16:41 +0800
From:	Bob Liu <lliubbo@...il.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	Sasha Levin <sasha.levin@...cle.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 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().

-- 
Regards,
--Bob
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