Re: mm: kernel BUG at mm/huge_memory.c:2785!

[Sasha Levin]

On 03/04/2014 10:16 PM, Bob Liu wrote:
> On Thu, Feb 27, 2014 at 11:03 PM, Kirill A. Shutemov
> <kirill.shutemov@xxxxxxxxxxxxxxx> 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.


Thanks,
Sasha
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