From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <SRS0=hmOx=2T=vger.kernel.org=bpf-owner@kernel.org>
X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on
	aws-us-west-2-korg-lkml-1.web.codeaurora.org
X-Spam-Level: 
X-Spam-Status: No, score=-7.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED,
	DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,
	MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1
	autolearn=unavailable autolearn_force=no version=3.4.0
Received: from mail.kernel.org (mail.kernel.org [198.145.29.99])
	by smtp.lore.kernel.org (Postfix) with ESMTP id 6C2B4C2D0DE
	for <bpf@archiver.kernel.org>; Sun, 29 Dec 2019 04:33:42 +0000 (UTC)
Received: from vger.kernel.org (vger.kernel.org [209.132.180.67])
	by mail.kernel.org (Postfix) with ESMTP id 42ABC21D7E
	for <bpf@archiver.kernel.org>; Sun, 29 Dec 2019 04:33:42 +0000 (UTC)
Authentication-Results: mail.kernel.org;
	dkim=pass (2048-bit key) header.d=nvidia.com header.i=@nvidia.com header.b="n7iOptnw"
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1726329AbfL2Edg (ORCPT <rfc822;bpf@archiver.kernel.org>);
        Sat, 28 Dec 2019 23:33:36 -0500
Received: from hqnvemgate26.nvidia.com ([216.228.121.65]:1482 "EHLO
        hqnvemgate26.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1726293AbfL2Edf (ORCPT <rfc822;bpf@vger.kernel.org>);
        Sat, 28 Dec 2019 23:33:35 -0500
Received: from hqpgpgate102.nvidia.com (Not Verified[216.228.121.13]) by hqnvemgate26.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA)
        id <B5e082c900000>; Sat, 28 Dec 2019 20:33:21 -0800
Received: from hqmail.nvidia.com ([172.20.161.6])
  by hqpgpgate102.nvidia.com (PGP Universal service);
  Sat, 28 Dec 2019 20:33:34 -0800
X-PGP-Universal: processed;
        by hqpgpgate102.nvidia.com on Sat, 28 Dec 2019 20:33:34 -0800
Received: from [10.110.48.28] (10.124.1.5) by HQMAIL107.nvidia.com
 (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Sun, 29 Dec
 2019 04:33:33 +0000
Subject: Re: [PATCH v11 00/25] mm/gup: track dma-pinned pages: FOLL_PIN
From:   John Hubbard <jhubbard@nvidia.com>
To:     Leon Romanovsky <leon@kernel.org>
CC:     Jason Gunthorpe <jgg@ziepe.ca>,
        Andrew Morton <akpm@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Alex Williamson <alex.williamson@redhat.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn.topel@intel.com>,
        Christoph Hellwig <hch@infradead.org>,
        Dan Williams <dan.j.williams@intel.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Dave Chinner <david@fromorbit.com>,
        David Airlie <airlied@linux.ie>,
        "David S . Miller" <davem@davemloft.net>,
        Ira Weiny <ira.weiny@intel.com>, Jan Kara <jack@suse.cz>,
        Jens Axboe <axboe@kernel.dk>, Jonathan Corbet <corbet@lwn.net>,
        =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>,
        Magnus Karlsson <magnus.karlsson@intel.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Michal Hocko <mhocko@suse.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Paul Mackerras <paulus@samba.org>,
        Shuah Khan <shuah@kernel.org>,
        Vlastimil Babka <vbabka@suse.cz>, <bpf@vger.kernel.org>,
        <dri-devel@lists.freedesktop.org>, <kvm@vger.kernel.org>,
        <linux-block@vger.kernel.org>, <linux-doc@vger.kernel.org>,
        <linux-fsdevel@vger.kernel.org>, <linux-kselftest@vger.kernel.org>,
        <linux-media@vger.kernel.org>, <linux-rdma@vger.kernel.org>,
        <linuxppc-dev@lists.ozlabs.org>, <netdev@vger.kernel.org>,
        <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>,
        Maor Gottlieb <maorg@mellanox.com>,
        "Ran Rozenstein" <ranro@mellanox.com>
References: <20191216222537.491123-1-jhubbard@nvidia.com>
 <20191219132607.GA410823@unreal>
 <a4849322-8e17-119e-a664-80d9f95d850b@nvidia.com>
 <20191219210743.GN17227@ziepe.ca> <20191220182939.GA10944@unreal>
 <1001a5fc-a71d-9c0f-1090-546c4913d8a2@nvidia.com>
 <20191222132357.GF13335@unreal>
 <49d57efe-85e1-6910-baf5-c18df1382206@nvidia.com>
 <20191225052612.GA212002@unreal>
 <b879d191-a07c-e808-e48f-2b9bd8ba4fa3@nvidia.com>
X-Nvconfidentiality: public
Message-ID: <612aa292-ec45-295c-b56c-c622876620fa@nvidia.com>
Date:   Sat, 28 Dec 2019 20:33:32 -0800
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.3.1
MIME-Version: 1.0
In-Reply-To: <b879d191-a07c-e808-e48f-2b9bd8ba4fa3@nvidia.com>
X-Originating-IP: [10.124.1.5]
X-ClientProxiedBy: HQMAIL111.nvidia.com (172.20.187.18) To
 HQMAIL107.nvidia.com (172.20.187.13)
Content-Type: text/plain; charset="utf-8"
Content-Language: en-US
Content-Transfer-Encoding: quoted-printable
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1;
        t=1577594001; bh=CS/Y1CGyDS+9QLfc4LRardH5VS56W/PAJOyfRY2LjTc=;
        h=X-PGP-Universal:Subject:From:To:CC:References:X-Nvconfidentiality:
         Message-ID:Date:User-Agent:MIME-Version:In-Reply-To:
         X-Originating-IP:X-ClientProxiedBy:Content-Type:Content-Language:
         Content-Transfer-Encoding;
        b=n7iOptnwN3ZVsCu/0DXie5ShRcR4/jOzIn6W7P3uTBxVaZt8ko4Dms+OE9l2tNSxe
         95GOtrfVtIDr0VsAlD/d/zPWSpFCkJY5UP5Eb2ss2F3NEgv4iTUN6NL2VHU+RtQqVi
         nFPi4CTJq0hll0B94/tPBP/T736se/ycwi7dWWtNiIfcgsX/aG2ZU9RUFFoSuSYe5B
         fwPDB3yWJZmxzNFs+zKaKVZ1e+/lnxSIdtwRl5XP/Vm1rz2l41lunDXgCSZTy/8O/h
         ByGzcgSVg+SF9TRzjsSZ/pWRsIBTO2VIGDe+IjvB1qU+Q0EIsH+JijQJxdtnLBWoeO
         bb0/oQMKrQ56Q==
Sender: bpf-owner@vger.kernel.org
Precedence: bulk
List-ID: <bpf.vger.kernel.org>
X-Mailing-List: bpf@vger.kernel.org

On 12/27/19 1:56 PM, John Hubbard wrote:
...
>> It is ancient verification test (~10y) which is not an easy task to
>> make it understandable and standalone :).
>>
>=20
> Is this the only test that fails, btw? No other test failures or hints of
> problems?
>=20
> (Also, maybe hopeless, but can *anyone* on the RDMA list provide some
> characterization of the test, such as how many pins per page, what page
> sizes are used? I'm still hoping to write a test to trigger something
> close to this...)
>=20
> I do have a couple more ideas for test runs:
>=20
> 1. Reduce GUP_PIN_COUNTING_BIAS to 1. That would turn the whole override =
of
> page->_refcount into a no-op, and so if all is well (it may not be!) with=
 the
> rest of the patch, then we'd expect this problem to not reappear.
>=20
> 2. Active /proc/vmstat *foll_pin* statistics unconditionally (just for th=
ese
> tests, of course), so we can see if there is a get/put mismatch. However,=
 that
> will change the timing, and so it must be attempted independently of (1),=
 in
> order to see if it ends up hiding the repro.
>=20
> I've updated this branch to implement (1), but not (2), hoping you can gi=
ve
> this one a spin?
>=20
> =C2=A0=C2=A0=C2=A0 git@github.com:johnhubbard/linux.git=C2=A0 pin_user_pa=
ges_tracking_v11_with_diags
>=20
>=20

Also, looking ahead:

a) if the problem disappears with the latest above test, then we likely hav=
e
   a huge page refcount overflow, and there are a couple of different ways =
to
   fix it.=20

b) if it still reproduces with the above, then it's some other random mista=
ke,
   and in that case I'd be inclined to do a sort of guided (or classic, ung=
uided)
   git bisect of the series. Because it could be any of several patches.

   If that's too much trouble, then I'd have to fall back to submitting a f=
ew
   patches at a time and working my way up to the tracking patch...


thanks,
--=20
John Hubbard
NVIDIA