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Re: Sleeping BUG in khugepaged for i586

From Michal Hocko <mhocko@kernel.org>
Newsgroups linux.kernel
Subject Re: Sleeping BUG in khugepaged for i586
Date 2017-06-15 10:40 +0200
Message-ID <tSytQ-8X-11@gated-at.bofh.it> (permalink)
References (3 earlier) <tPohj-20d-3@gated-at.bofh.it> <tPDq2-3rU-31@gated-at.bofh.it> <tPQdA-38j-17@gated-at.bofh.it> <tQ6V4-5vT-13@gated-at.bofh.it> <tSrC1-4gc-7@gated-at.bofh.it>
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On Wed 14-06-17 18:12:06, David Rientjes wrote:
> On Thu, 8 Jun 2017, Michal Hocko wrote:
> 
> > 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.
> > 
> 
> Seems to be an issue for i386 and arm with ARM_LPAE.  I'm slightly 
> surprised we can get away with __collapse_huge_page_swapin() for 
> VM_FAULT_RETRY, unless that hasn't been encountered yet.

I do not see what you mean here or how is it related.
__collapse_huge_page_swapin is called outside of
pte_offset_map/pte_unmap section

> I think the cond_resched() in __collapse_huge_page_copy() could be
> done only for !in_atomic() if we choose.

in_atomic() depends on having PREEMPT_COUNT enabled to work properly AFAIR.
I haven't double checked and something might have changed since I've
looked the last time.

-- 
Michal Hocko
SUSE Labs

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Thread

Re: Sleeping BUG in khugepaged for i586 David Rientjes <rientjes@google.com> - 2017-06-07 23:00 +0200
  Re: Sleeping BUG in khugepaged for i586 Michal Hocko <mhocko@kernel.org> - 2017-06-08 16:50 +0200
    Re: Sleeping BUG in khugepaged for i586 Matthew Wilcox <willy@infradead.org> - 2017-06-08 19:10 +0200
      Re: Sleeping BUG in khugepaged for i586 Michal Hocko <mhocko@kernel.org> - 2017-06-08 22:20 +0200
        Re: Sleeping BUG in khugepaged for i586 Michal Hocko <mhocko@kernel.org> - 2017-06-08 22:40 +0200
          Re: Sleeping BUG in khugepaged for i586 Vlastimil Babka <vbabka@suse.cz> - 2017-06-09 08:50 +0200
            Re: Sleeping BUG in khugepaged for i586 Michal Hocko <mhocko@kernel.org> - 2017-06-09 09:50 +0200
            Re: Sleeping BUG in khugepaged for i586 Larry Finger <Larry.Finger@lwfinger.net> - 2017-06-09 16:30 +0200
          Re: Sleeping BUG in khugepaged for i586 David Rientjes <rientjes@google.com> - 2017-06-10 00:40 +0200
            Re: Sleeping BUG in khugepaged for i586 Michal Hocko <mhocko@kernel.org> - 2017-06-10 10:10 +0200
              Re: Sleeping BUG in khugepaged for i586 David Rientjes <rientjes@google.com> - 2017-06-12 01:30 +0200
                Re: Sleeping BUG in khugepaged for i586 Michal Hocko <mhocko@kernel.org> - 2017-06-12 08:30 +0200
                Re: Sleeping BUG in khugepaged for i586 David Rientjes <rientjes@google.com> - 2017-06-15 02:30 +0200
    Re: Sleeping BUG in khugepaged for i586 David Rientjes <rientjes@google.com> - 2017-06-15 03:20 +0200
      Re: Sleeping BUG in khugepaged for i586 Michal Hocko <mhocko@kernel.org> - 2017-06-15 10:40 +0200
  Re: Sleeping BUG in khugepaged for i586 Larry Finger <Larry.Finger@lwfinger.net> - 2017-06-08 17:30 +0200

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