linux-kernel - Re: [PATCH 1/2] mm: introduce put_user

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Message-ID: <9c1985cc-cd99-a950-5ea2-9df9f93eb98b@nvidia.com>
Date:   Fri, 8 Feb 2019 12:44:48 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Mike Rapoport <rppt@...ux.ibm.com>, <john.hubbard@...il.com>
CC:     Andrew Morton <akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christian Benvenuti <benve@...co.com>,
        Christoph Hellwig <hch@...radead.org>,
        Christopher Lameter <cl@...ux.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Dennis Dalessandro <dennis.dalessandro@...el.com>,
        Doug Ledford <dledford@...hat.com>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jerome Glisse <jglisse@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...nel.org>,
        Mike Marciniszyn <mike.marciniszyn@...el.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Tom Talpey <tom@...pey.com>,
        LKML <linux-kernel@...r.kernel.org>,
        <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 1/2] mm: introduce put_user_page*(), placeholder versions

On 2/8/19 2:32 AM, Mike Rapoport wrote:
> On Thu, Feb 07, 2019 at 11:56:48PM -0800, john.hubbard@...il.com wrote:
>> From: John Hubbard <jhubbard@...dia.com>
[...]
>> +/**
>> + * put_user_page() - release a gup-pinned page
>> + * @page:            pointer to page to be released
>> + *
>> + * Pages that were pinned via get_user_pages*() must be released via
>> + * either put_user_page(), or one of the put_user_pages*() routines
>> + * below. This is so that eventually, pages that are pinned via
>> + * get_user_pages*() can be separately tracked and uniquely handled. In
>> + * particular, interactions with RDMA and filesystems need special
>> + * handling.
>> + *
>> + * put_user_page() and put_page() are not interchangeable, despite this early
>> + * implementation that makes them look the same. put_user_page() calls must
> 
> I just hope we'll remember to update when the real implementation will be
> merged ;-)
> 
> Other than that, feel free to add
> 
> Reviewed-by: Mike Rapoport <rppt@...ux.ibm.com>	# docs
> 

Thanks for the review!

Yes, the follow-on patch that turns this into a real implementation is
posted [1], and its documentation is updated accordingly.

(I've already changed "@Returns" to "@Return" locally in that patch, btw.)

[1] https://lore.kernel.org/r/20190204052135.25784-5-jhubbard@nvidia.com

thanks,
-- 
John Hubbard
NVIDIA