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

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Message-ID: <alpine.LSU.2.11.1510211744380.5219@eggly.anvils>
Date:	Wed, 21 Oct 2015 17:59:59 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Minchan Kim <minchan@...nel.org>
cc:	"Kirill A. Shutemov" <kirill@...temov.name>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Vlastimil Babka <vbabka@...e.cz>
Subject: Re: kernel oops on mmotm-2015-10-15-15-20

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.

> 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.

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.

Hugh
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