linux-kernel - Re: [PATCH v7 2/8] iov_iter: Add a function to extract a page list from an iterator

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Message-ID: <3814749.1674474663@warthog.procyon.org.uk>
Date:   Mon, 23 Jan 2023 11:51:03 +0000
From:   David Howells <dhowells@...hat.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     dhowells@...hat.com, Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, Christoph Hellwig <hch@....de>,
        John Hubbard <jhubbard@...dia.com>, linux-mm@...ck.org
Subject: Re: [PATCH v7 2/8] iov_iter: Add a function to extract a page list from an iterator

David Hildenbrand <david@...hat.com> wrote:

> How does this work align with the goal of no longer using FOLL_GET for
> O_DIRECT? We should get rid of any FOLL_GET usage for accessing page content.

Would that run the risk of changes being made by the child being visible to
the a DIO write if the parent changes the buffer first?


	PARENT			CHILD
	======			=====
	start-DIO-write
	fork() = pid		fork() = 0
	alter-buffer
	CoW happens
	page copied		original page retained
				alter-buffer
		<DMA-happens>

David