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

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Date:   Wed, 10 Oct 2018 16:43:59 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Jan Kara <jack@...e.cz>, <john.hubbard@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...nel.org>,
        Christopher Lameter <cl@...ux.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        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 Tue, 9 Oct 2018 17:32:16 -0700 John Hubbard <jhubbard@...dia.com> wrote:

> > I'm not really understanding.  Patch 3/3 changes just one infiniband
> > driver to use put_user_page().  But the changelogs here imply (to me)
> > that every user of get_user_pages() needs to be converted to
> > s/put_page/put_user_page/.
> > 
> > Methinks a bit more explanation is needed in these changelogs?
> > 
> 
> OK, yes, it does sound like the explanation is falling short. I'll work on something 
> clearer. Did the proposed steps in the changelogs, such as:
>   
> [2] https://lkml.kernel.org/r/20180709080554.21931-1-jhubbard@nvidia.com
>     Proposed steps for fixing get_user_pages() + DMA problems.
> 
> help at all, or is it just too many references, and I should write the words
> directly in the changelog?
> 
> Anyway, patch 3/3 is a just a working example (which we do want to submit, though), and
> many more conversions will follow. But they don't have to be done all upfront--they
> can be done in follow up patchsets. 
> 
> The put_user_page*() routines are, at this point, not going to significantly change
> behavior. 
> 
> I'm working on an RFC that will show what the long-term fix to get_user_pages and
> put_user_pages will look like. But meanwhile it's good to get started on converting
> all of the call sites.

I see.  Yes, please do put all of it into the changelog[s].