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[216.228.121.143]) by mx.google.com with ESMTPS id r82si37492pfa.140.2019.03.14.13.37.07 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 14 Mar 2019 13:37:07 -0700 (PDT) Received-SPF: pass (google.com: domain of jhubbard@nvidia.com designates 216.228.121.143 as permitted sender) client-ip=216.228.121.143; Authentication-Results: mx.google.com; dkim=pass header.i=@nvidia.com header.s=n1 header.b=jpTdb9Oc; spf=pass (google.com: domain of jhubbard@nvidia.com designates 216.228.121.143 as permitted sender) smtp.mailfrom=jhubbard@nvidia.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=nvidia.com Received: from hqpgpgate101.nvidia.com (Not Verified[216.228.121.13]) by hqemgate14.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; 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 , Jan Kara CC: Jason Gunthorpe , Christopher Lameter , Jerome Glisse , , Andrew Morton , , Al Viro , Christian Benvenuti , Christoph Hellwig , Dan Williams , Dave Chinner , Dennis Dalessandro , Doug Ledford , Ira Weiny , Matthew Wilcox , Michal Hocko , Mike Rapoport , Mike Marciniszyn , Ralph Campbell , Tom Talpey , LKML , 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 X-Nvconfidentiality: public Message-ID: 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== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 3/14/19 1:25 PM, William Kucharski wrote: > > >> On Mar 14, 2019, at 7:30 AM, Jan Kara 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. >