linux-kernel - Re: [PATCH v4 2/3] mm: introduce put_user

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Message-ID: <4f47f3d4-1b00-e534-309c-7fb044337040@nvidia.com>
Date:   Sun, 4 Nov 2018 23:25:31 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Jan Kara <jack@...e.cz>
CC:     Jason Gunthorpe <jgg@...pe.ca>,
        Andrew Morton <akpm@...ux-foundation.org>,
        <john.hubbard@...il.com>, Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...nel.org>,
        Christopher Lameter <cl@...ux.com>,
        Dan Williams <dan.j.williams@...el.com>, <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-rdma <linux-rdma@...r.kernel.org>,
        <linux-fsdevel@...r.kernel.org>, Al Viro <viro@...iv.linux.org.uk>,
        "Jerome Glisse" <jglisse@...hat.com>,
        Christoph Hellwig <hch@...radead.org>,
        "Ralph Campbell" <rcampbell@...dia.com>
Subject: Re: [PATCH v4 2/3] mm: introduce put_user_page*(), placeholder
 versions

On 10/18/18 3:19 AM, Jan Kara wrote:
> On Thu 11-10-18 20:53:34, John Hubbard wrote:
>> On 10/11/18 6:23 PM, John Hubbard wrote:
>>> On 10/11/18 6:20 AM, Jason Gunthorpe wrote:
>>>> On Thu, Oct 11, 2018 at 10:49:29AM +0200, Jan Kara wrote:
[...]
> Well, put_page() cannot assert page is not dma-pinned as someone can still
> to get_page(), put_page() on dma-pinned page and that must not barf. But
> put_page() could assert that if the page is pinned, refcount is >=
> pincount. That will detect leaked pin references relatively quickly.
> 

That assertion is definitely a life saver. I've been attempting a combination
of finishing up more call site conversions, and runtime testing, and this
lights up the missing conversions pretty nicely.

As I mentioned in another thread just now, I'll send out an updated RFC this week,
so that people can look through it well before the LPC (next week).

thanks,
-- 
John Hubbard
NVIDIA