Re: Sleeping BUG in khugepaged for i586

Michal Hocko
2017-06-23T12:08:17Z

On Thu 08-06-17 16:48:31, Michal Hocko wrote:
> On Wed 07-06-17 13:56:01, David Rientjes wrote:
> > On Wed, 7 Jun 2017, Vlastimil Babka wrote:
> >
> > > >> Hmm I'd expect such spin lock to be reported together with mmap_sem in
> > > >> the debugging "locks held" message?
> > > >
> > > > My bisection of the problem is about half done. My latest good version is commit
> > > > 7b8cd33 and the latest bad one is 2ea659a. Only about 7 steps to go.
> > >
> > > Hmm, your bisection will most likely just find commit 338a16ba15495
> > > which added the cond_resched() at mm/khugepaged.c:655. CCing David who
> > > added it.
> > >
> >
> > I agree it's probably going to bisect to 338a16ba15495 since it's the
> > cond_resched() at the line number reported, but I think there must be
> > something else going on. I think the list of locks held by khugepaged is
> > correct because it matches with the implementation. The preempt_count(),
> > as suggested by Andrew, does not. If this is reproducible, I'd like to
> > know what preempt_count() is.
>
> collapse_huge_page
> pte_offset_map
> kmap_atomic
> kmap_atomic_prot
> preempt_disable
> __collapse_huge_page_copy
> pte_unmap
> kunmap_atomic
> __kunmap_atomic
> preempt_enable
>
> I suspect, so cond_resched seems indeed inappropriate on 32b systems.

The code still seems to be in the mmotm tree. Are there any plans to fix
this or drop the patch?
--
Michal Hocko
SUSE Labs