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From: valdis.kletnieks@vt.edu
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X-Mailer: exmh version 2.8.0 04/21/2017 with nmh-1.6+dev
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>,
        Punit Agrawal <punit.agrawal@arm.com>,
        Steve Capper <steve.capper@arm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
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        LKML <linux-kernel@vger.kernel.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Cyrill Gorcunov <gorcunov@openvz.org>
Subject: Re: linux-next: BUG: Bad page state in process ip6tables-save pfn:1499f4
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Date: Tue, 27 Jun 2017 14:39:53 -0400
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On Tue, 27 Jun 2017 19:37:34 +0300, "Kirill A. Shutemov" said:

> > > commit c3aab7b2d4e8434d53bc81770442c14ccf0794a8
> > > Merge: 849c34f 93a7379
> > > Author: Stephen Rothwell
> > > Date:   Fri Jun 23 16:40:07 2017 +1000
> > >
> > >     Merge branch 'akpm-current/current'
> >
> > Hm is it really the merge of mmotm itself and not one of the patches in
> > mmotm?
> > Anyway smells like THP, adding Kirill.
>
> Okay, it took a while to figure it out.
>
> The bug is in patch "mm, gup: ensure real head page is ref-counted when
> using hugepages". We should look for a head *before* the loop. Otherwise
> 'page' may point to the first page beyond the compound page.
>
> The patch below should help.

Confirmed that fixes the BUGs that I was hitting.

Tested-By: Valdis Kletnieks <valdis.kletnieks@vt.edu>

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