linux-kernel - Re: linux-next: BUG: Bad page state in process ip6tables-save pfn:1499f4

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Message-ID: <8643.1498588793@turing-police.cc.vt.edu>
Date:   Tue, 27 Jun 2017 14:39:53 -0400
From:   valdis.kletnieks@...edu
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        Punit Agrawal <punit.agrawal@....com>,
        Steve Capper <steve.capper@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrei Vagin <avagin@...il.com>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Cyrill Gorcunov <gorcunov@...nvz.org>
Subject: Re: linux-next: BUG: Bad page state in process ip6tables-save pfn:1499f4

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@...edu>

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