Re: Sleeping BUG in khugepaged for i586

David Rientjes
2017-06-07T20:56:05Z

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.