Re: kernel oops on mmotm-2015-10-15-15-20

[Hugh Dickins <hughd@google.com>]

On Thu, 22 Oct 2015, Minchan Kim wrote:
> Hello Hugh,
> 
> On Wed, Oct 21, 2015 at 05:59:59PM -0700, Hugh Dickins wrote:
> > On Thu, 22 Oct 2015, Minchan Kim wrote:
> > > 
> > > I added the code to check it and queued it again but I had another oops
> > > in this time but symptom is related to anon_vma, too.
> > > (kernel is based on recent mmotm + unconditional mkdirty for bug fix)
> > > It seems page_get_anon_vma returns NULL since the page was not page_mapped
> > > at that time but second check of page_mapped right before try_to_unmap seems
> > > to be true.
> > > 
> > > Adding 4191228k swap on /dev/vda5.  Priority:-1 extents:1 across:4191228k FS
> > > Adding 4191228k swap on /dev/vda5.  Priority:-1 extents:1 across:4191228k FS
> > > page:ffffea0001cfbfc0 count:3 mapcount:1 mapping:ffff88007f1b5f51 index:0x600000aff
> > > flags: 0x4000000000048019(locked|uptodate|dirty|swapcache|swapbacked)
> > > page dumped because: VM_BUG_ON_PAGE(PageAnon(page) && !PageKsm(page) && !anon_vma)
> > 
> > That's interesting, that's one I added in my page migration series.
> > Let me think on it, but it could well relate to the one you got before.
> 
> I will roll back to mm/madv_free-v4.3-rc5-mmotm-2015-10-15-15-20
> instead of next-20151021 to remove noise from your migration cleanup
> series and will test it again.
> If it is fixed, I will test again with your migration patchset, then.

Not a good use of your time, I think.  It's sure to be fixed in the
rc5-mmotm because that VM_BUG_ON_PAGE(blah) just does not exist in
that tree: I added it to verify my reasoning in changing the comments
about page_get_anon_vma() and PageSwapCache in mm/migrate.c.

> 
> > 
> > > page->mem_cgroup:ffff88007f3dcc00
> > > ------------[ cut here ]------------
> > > kernel BUG at mm/migrate.c:889!
> > > invalid opcode: 0000 [#1] SMP 
> > > Dumping ftrace buffer:
> > >    (ftrace buffer empty)
> > > Modules linked in:
> > > CPU: 11 PID: 59 Comm: khugepaged Not tainted 4.3.0-rc6-next-20151021-THP-ref-madv_free+ #1557
> > 
> > Hmm, it might be me to blame, or it might be Kirill, don't know yet.
> 
> It might be me, either.
> 
> > 
> > Oh, hold on, I think Andrew has just posted a new mmotm, and it includes
> > an update to Kirill's migrate_pages-try-to-split-pages-on-queueing.patch:
> > I haven't digested yet, but it might turn out to be relevant.

Sorry, I think that was an irrelevant suggestion: today's new rc6-mmotm
is identical to yesterday's there, and the patch that was removed appears
to be identical to the one added.

Hugh

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