netdev - Re: [PATCH 3/3] net/xdp: convert put_page() to put_user

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Date:   Tue, 23 Jul 2019 16:24:23 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Ira Weiny <ira.weiny@...el.com>
CC:     <john.hubbard@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Björn Töpel <bjorn.topel@...el.com>,
        Boaz Harrosh <boaz@...xistor.com>,
        Christoph Hellwig <hch@....de>,
        Daniel Vetter <daniel@...ll.ch>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        David Airlie <airlied@...ux.ie>,
        "David S . Miller" <davem@...emloft.net>,
        Ilya Dryomov <idryomov@...il.com>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>, Jens Axboe <axboe@...nel.dk>,
        Jérôme Glisse <jglisse@...hat.com>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Matthew Wilcox <willy@...radead.org>,
        Miklos Szeredi <miklos@...redi.hu>,
        Ming Lei <ming.lei@...hat.com>, Sage Weil <sage@...hat.com>,
        Santosh Shilimkar <santosh.shilimkar@...cle.com>,
        Yan Zheng <zyan@...hat.com>, <netdev@...r.kernel.org>,
        <dri-devel@...ts.freedesktop.org>, <linux-mm@...ck.org>,
        <linux-rdma@...r.kernel.org>, <bpf@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] net/xdp: convert put_page() to put_user_page*()

On 7/23/19 11:06 AM, Ira Weiny wrote:
> On Mon, Jul 22, 2019 at 09:41:34PM -0700, John Hubbard wrote:
>> On 7/22/19 5:25 PM, Ira Weiny wrote:
>>> On Mon, Jul 22, 2019 at 03:34:15PM -0700, john.hubbard@...il.com wrote:
...
>> Obviously, this stuff is all subject to a certain amount of opinion, but I
>> think I'm on really solid ground as far as precedent goes. So I'm pushing
>> back on the NAK... :)
> 
> Fair enough...  However, we have discussed in the past how GUP can be a
> confusing interface to use.
> 
> So I'd like to see it be more directed.  Only using the __put_user_pages()
> version allows us to ID callers easier through a grep of PUP_FLAGS_DIRTY_LOCK
> in addition to directing users to use that interface rather than having to read
> the GUP code to figure out that the 2 calls above are equal.  It is not a huge
> deal but...
> 

OK, combining all the feedback to date, which is:

* the leading double underscore is unloved,

* set_page_dirty() is under investigation, but likely guilty of incitement
  to cause bugs,


...we end up with this:

void put_user_pages_dirty_lock(struct page **pages, unsigned long npages,
			       bool make_dirty)

...which I have a v2 patchset for, ready to send out. It makes IB all pretty 
too. :)


thanks,
-- 
John Hubbard
NVIDIA