Re: [patch] hugetlb: fix lockdep error

[Nick Piggin <npiggin@suse.de>]

On Wed, May 28, 2008 at 08:19:29PM -0700, Andrew Morton 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.

Could be it was ignored as a false positive?

 
> If that's really the case then perhaps we should make the ability to
> recite Documentation/SubmitChecklist in three languages a prerequisite
> for MM development.

It does seem unusual, I don't know...

Would it help to have a big button in kconfig called "test your kernel
patches with this", which then selects various other things?

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