Re: [patch] hugetlb: fix lockdep error

["Nish Aravamudan" <nish.aravamudan@gmail.com>]

On 5/28/08, Andrew Morton <akpm@linux-foundation.org> wrote:
> On Thu, 29 May 2008 05:07:45 +0200 Nick Piggin <npiggin@suse.de> wrote:
>
>  > > >  mm/hugetlb.c |    2 +-
>  > > >  1 file changed, 1 insertion(+), 1 deletion(-)
>  > > >
>  > > > Index: linux-2.6/mm/hugetlb.c
>  > > > ===================================================================
>  > > > --- linux-2.6.orig/mm/hugetlb.c
>  > > > +++ linux-2.6/mm/hugetlb.c
>  > > > @@ -785,7 +785,7 @@ int copy_hugetlb_page_range(struct mm_st
>  > > >                   continue;
>  > > >
>  > > >           spin_lock(&dst->page_table_lock);
>  > > > -         spin_lock(&src->page_table_lock);
>  > > > +         spin_lock_nested(&src->page_table_lock, SINGLE_DEPTH_NESTING);
>  > > >           if (!huge_pte_none(huge_ptep_get(src_pte))) {
>  > > >                   if (cow)
>  > > >                           huge_ptep_set_wrprotect(src, addr, src_pte);
>  > >
>  > > Confused.  This code has been there since October 2005.  Why are we
>  > > only seeing lockdep warnings now?
>  >
>  > Can't say. Haven't looked at hugetlb code or tested it much until now.
>  > I am using a recent libhugetlbfs test suite, FWIW.
>
>
> I don't believe that it's possible that nobody has run that test suite
>  with lockdep enabled at any time in the past three years.

I can't tell from Nick's mail if the lockdep error is specific to this
particular testcase or not, but if so, that would make it the past two
(almost three) months, as that was when this particular testcase was
added. And I'm not sure when we released the first development
snapshot that would have included it (for non-git users, that is). In
any case, I also don't know how we wouldn't have seen this issue on
our systems and that's a problem. I will make a concerted effort to
work with the other libhugetlbfs developers to make sure all possible
debug options are on (as you've pointed out to me elsewhere/when).


Thanks,
Nish

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