Received: by 2002:ac0:950c:0:0:0:0:0 with SMTP id f12csp4151205imc;
        Thu, 14 Mar 2019 13:38:05 -0700 (PDT)
X-Google-Smtp-Source: APXvYqwySXpdBc16eWnbNOh/X01autEZW6DfqDMJ6gAMf9/7UHmshY3TE5SprcysXJq+tZ1BwfAY
X-Received: by 2002:a63:4718:: with SMTP id u24mr47593767pga.381.1552595884915;
        Thu, 14 Mar 2019 13:38:04 -0700 (PDT)
ARC-Seal: i=1; a=rsa-sha256; t=1552595884; cv=none;
        d=google.com; s=arc-20160816;
        b=mnh9cYJyX9R6kvrDcMtosrdlAvAuO7uxIlIAmhyFKSsWUh1RquA9j/5FNHVfTx3oji
         dSI1+prDQ/K2K/4C7A/MI2bKBShXHwcTg69rEj00tckKhnHSa9aRAEGgchDkooR3onIF
         87wUAJwNJ4ufnz18czCEa15hgrP6TxOsQ5lbYROnxVvXd4564oGM/6Greosydyd+qqS5
         zEUkNI6hYlSWp5L6tA388cpH3snJdU5S6qmWuTrhUnGpUDnMtpyqJyWmjeZgzpKc8t1X
         UlFnb4Itq07WGIwfcOvUHuHI8SikzefPW/MAH9J+FoO5Zgsq28OcUPcFIeR5IqUaTyQ4
         lPqA==
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816;
        h=list-id:precedence:sender:dkim-signature:content-transfer-encoding
         :content-language:in-reply-to:mime-version:user-agent:date
         :message-id:from:references:cc:to:subject;
        bh=DgWsHZ14WtEAfPFOWW1z2Gf+RMCUzw4CBvC7Or4dKYg=;
        b=YXACiNSDQOr67VBYkwH/SfMDtUUoAnIGjL80iyCWvNMc03wrXC0rh3rr3BbTYEaza8
         FBGwYgbFZlgbsypQ4o4uJjlcf79owYjfcbsvGNOnu3mnEYeCJ7zrjcz9tcg4m8PnNQgs
         KqtB//+pJ6EvdhKbXBVRyIWwC1VjvaOh3vqcAMt4Lb4/crNeseBEG7g19r6gHARCEnpK
         V7GGdd8SsAC7bqUREoPZ9jHuQw096qElBbTCFdMm+PNnr/bo59E4JqO+hdnhAmyd/jJL
         7ypwKa20DyhEAez47uZus8lEjiYiUW8Esk5BDGerNCgyUzm+VVc84Eyla8ZWcfHnqkNf
         n7Bw==
ARC-Authentication-Results: i=1; mx.google.com;
       dkim=pass header.i=@nvidia.com header.s=n1 header.b=jpTdb9Oc;
       spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org;
       dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=nvidia.com
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: from vger.kernel.org (vger.kernel.org. [209.132.180.67])
        by mx.google.com with ESMTP id s139si13221576pgs.405.2019.03.14.13.37.48;
        Thu, 14 Mar 2019 13:38:04 -0700 (PDT)
Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Authentication-Results: mx.google.com;
       dkim=pass header.i=@nvidia.com header.s=n1 header.b=jpTdb9Oc;
       spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org;
       dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=nvidia.com
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1727779AbfCNUhH (ORCPT <rfc822;brice.berna@gmail.com>
        + 99 others); Thu, 14 Mar 2019 16:37:07 -0400
Received: from hqemgate14.nvidia.com ([216.228.121.143]:18794 "EHLO
        hqemgate14.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1727480AbfCNUhH (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Thu, 14 Mar 2019 16:37:07 -0400
Received: from hqpgpgate101.nvidia.com (Not Verified[216.228.121.13]) by hqemgate14.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA)
        id <B5c8abb740000>; Thu, 14 Mar 2019 13:37:08 -0700
Received: from hqmail.nvidia.com ([172.20.161.6])
  by hqpgpgate101.nvidia.com (PGP Universal service);
  Thu, 14 Mar 2019 13:37:06 -0700
X-PGP-Universal: processed;
        by hqpgpgate101.nvidia.com on Thu, 14 Mar 2019 13:37:06 -0700
Received: from ngvpn01-165-234.dyn.scz.us.nvidia.com (10.124.1.5) by
 HQMAIL101.nvidia.com (172.20.187.10) with Microsoft SMTP Server (TLS) id
 15.0.1473.3; Thu, 14 Mar 2019 20:37:06 +0000
Subject: Re: [PATCH v3 0/1] mm: introduce put_user_page*(), placeholder
 versions
To:     William Kucharski <william.kucharski@oracle.com>,
        Jan Kara <jack@suse.cz>
CC:     Jason Gunthorpe <jgg@ziepe.ca>, Christopher Lameter <cl@linux.com>,
        Jerome Glisse <jglisse@redhat.com>, <john.hubbard@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        <linux-mm@kvack.org>, Al Viro <viro@zeniv.linux.org.uk>,
        Christian Benvenuti <benve@cisco.com>,
        Christoph Hellwig <hch@infradead.org>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Chinner <david@fromorbit.com>,
        Dennis Dalessandro <dennis.dalessandro@intel.com>,
        Doug Ledford <dledford@redhat.com>,
        Ira Weiny <ira.weiny@intel.com>,
        Matthew Wilcox <willy@infradead.org>,
        Michal Hocko <mhocko@kernel.org>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Mike Marciniszyn <mike.marciniszyn@intel.com>,
        Ralph Campbell <rcampbell@nvidia.com>,
        Tom Talpey <tom@talpey.com>,
        LKML <linux-kernel@vger.kernel.org>,
        <linux-fsdevel@vger.kernel.org>
References: <20190306235455.26348-1-jhubbard@nvidia.com>
 <010001695b4631cd-f4b8fcbf-a760-4267-afce-fb7969e3ff87-000000@email.amazonses.com>
 <20190308190704.GC5618@redhat.com>
 <01000169703e5495-2815ba73-34e8-45d5-b970-45784f653a34-000000@email.amazonses.com>
 <20190312153528.GB3233@redhat.com>
 <01000169787c61d0-cbc5486e-960a-492f-9ac9-9f6a466efeed-000000@email.amazonses.com>
 <20190314090345.GB16658@quack2.suse.cz> <20190314125718.GO20037@ziepe.ca>
 <20190314133038.GJ16658@quack2.suse.cz>
 <3AF66C8F-F4BC-4413-A01C-3C90A3C27B28@oracle.com>
From:   John Hubbard <jhubbard@nvidia.com>
X-Nvconfidentiality: public
Message-ID: <b3090734-7250-8ee6-8c15-661ad8177c11@nvidia.com>
Date:   Thu, 14 Mar 2019 13:37:05 -0700
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:60.0)
 Gecko/20100101 Thunderbird/60.5.3
MIME-Version: 1.0
In-Reply-To: <3AF66C8F-F4BC-4413-A01C-3C90A3C27B28@oracle.com>
X-Originating-IP: [10.124.1.5]
X-ClientProxiedBy: HQMAIL108.nvidia.com (172.18.146.13) To
 HQMAIL101.nvidia.com (172.20.187.10)
Content-Type: text/plain; charset="utf-8"; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1;
        t=1552595828; bh=DgWsHZ14WtEAfPFOWW1z2Gf+RMCUzw4CBvC7Or4dKYg=;
        h=X-PGP-Universal:Subject:To:CC:References:From: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=jpTdb9OciKuyWNtxC/d1OlI3Sd/Cq6Uwi8BEbaAuli5lMpDCFIslwzEtCyWQ5s9pP
         yag3egLlxKb8JoNaDiA5B3fNolLhyACXMoRdr/CfWKdrXNxpa1KELCWTkXhllRS3o9
         Lt9cApp1NapXxvVHOb6o60T2AYiZinJGfejLmjcPv3B6e36Z5tlCoo7ZbWLmC+NUHP
         7PEcdjTc7yLcVPTB6YbHvX1zefygfGRi2pRuVIqA5zS5SAugjNEAnWO/Tdr3cprYNO
         SPIs3ifMB1H8GsXj+PnE3iEybhHN0PyHvCO/gOJBJgw3mRMbFwMwfyPs1FOj56faEv
         OFY3y4rNhAhLw==
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 3/14/19 1:25 PM, William Kucharski wrote:
> 
> 
>> On Mar 14, 2019, at 7:30 AM, Jan Kara <jack@suse.cz> wrote:
>>
>> Well I have some crash reports couple years old and they are not from QA
>> departments. So I'm pretty confident there are real users that use this in
>> production... and just reboot their machine in case it crashes.
> 
> Do you know what the use case in those crashes actually was?
> 
> I'm curious to know they were actually cases of say DMA from a video
> capture card or if the uses posited to date are simply theoretical.


It's not merely theoretical. In addition to Jan's bug reports, I've
personally investigated a bug that involved an GPU (acting basically as
an AI accelerator in this case) that was doing DMA to memory that turned
out to be file backed.

The backtrace for that is in the commit description.

As others have mentioned, this works well enough to lure people into
using it, but then fails when you load down a powerful system (and put
it under memory pressure).

I think that as systems get larger, and more highly threaded, we might
see more such failures--maybe even in the Direct IO case someday,
although so far that race window is so small that that one truly is
still theoretical (or, we just haven't been in communication with
anyone who hit it).

thanks,
-- 
John Hubbard
NVIDIA

> 
> It's always good to know who might be doing this and why if for no other
> reason than as something to keep in mind when designing future interfaces.
>