linux-kernel - Re: [PATCH 1/3] mm/gup: introduce __put_user

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Message-ID: <20190723055359.GC17148@lst.de>
Date:   Tue, 23 Jul 2019 07:53:59 +0200
From:   Christoph Hellwig <hch@....de>
To:     john.hubbard@...il.com
Cc:     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>,
        John Hubbard <jhubbard@...dia.com>
Subject: Re: [PATCH 1/3] mm/gup: introduce __put_user_pages()

On Mon, Jul 22, 2019 at 03:34:13PM -0700, john.hubbard@...il.com wrote:
> +enum pup_flags_t {
> +	PUP_FLAGS_CLEAN		= 0,
> +	PUP_FLAGS_DIRTY		= 1,
> +	PUP_FLAGS_LOCK		= 2,
> +	PUP_FLAGS_DIRTY_LOCK	= 3,
> +};

Well, the enum defeats the ease of just being able to pass a boolean
expression to the function, which would simplify a lot of the caller,
so if we need to support the !locked version I'd rather see that as
a separate helper.

But do we actually have callers where not using the _lock version is
not a bug?  set_page_dirty makes sense in the context of a file systems
that have a reference to the inode the page hangs off, but that is
(almost?) never the case for get_user_pages.