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Date: Tue, 17 Jun 2014 09:09:09 -0500 (CDT)
From: Christoph Lameter <cl@gentwo.org>
To: Sasha Levin <sasha.levin@oracle.com>
cc: Hugh Dickins <hughd@google.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Konstantin Khlebnikov <koct9i@gmail.com>, Mel Gorman <mgorman@suse.de>,
        Bob Liu <bob.liu@oracle.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>, Dave Jones <davej@redhat.com>
Subject: Re: mm: NULL ptr deref in remove_migration_pte
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Message-ID: <alpine.DEB.2.11.1406170907540.12946@gentwo.org>
References: <534E9ACA.2090008@oracle.com> <5367B365.1070709@oracle.com> <537FE9F3.40508@oracle.com> <alpine.LSU.2.11.1405261255530.3649@eggly.anvils> <538498A1.7010305@oracle.com> <alpine.LSU.2.11.1406092104330.12382@eggly.anvils>
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On Mon, 16 Jun 2014, Sasha Levin wrote:

> It took some time to hit something here, but I think that the following
> is related:

This related thing looks like someone did a random memset. The SLUB
diagnostic show the object, redzone and padding were overwritten with
zeros.

> [  494.710068] =============================================================================
> [  494.710068] BUG page->ptl (Not tainted): Redzone overwritten
> [  494.710068] -----------------------------------------------------------------------------
> [  494.710068]
> [  494.710068] INFO: 0xffff8804e4730e58-0xffff8804e4730e5f. First byte 0x0 instead of 0xbb
> [  494.710068] INFO: Slab 0xffffea001391cc00 objects=40 used=40 fp=0x          (null) flags=0x56fffff80004080
> [  494.710068] INFO: Object 0xffff8804e4730e10 @offset=3600 fp=0x          (null)
> [  494.710068]
> [  494.710068] Bytes b4 ffff8804e4730e00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> [  494.710068] Object ffff8804e4730e10: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> [  494.710068] Object ffff8804e4730e20: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> [  494.710068] Object ffff8804e4730e30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> [  494.710068] Object ffff8804e4730e40: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> [  494.710068] Object ffff8804e4730e50: 00 00 00 00 00 00 00 00                          ........
> [  494.710068] Redzone ffff8804e4730e58: 00 00 00 00 00 00 00 00                          ........
> [  494.710068] Padding ffff8804e4730f98: 00 00 00 00 00 00 00 00                          ........
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