linux-kernel - Re: [PATCH v20 00/32] splice, block: Use page pinning and kill ITER

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Date:   Fri, 19 May 2023 01:06:18 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Jens Axboe <axboe@...nel.dk>, Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Hillf Danton <hdanton@...a.com>,
        Christian Brauner <brauner@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v20 00/32] splice, block: Use page pinning and kill
 ITER_PIPE

On Fri, May 19, 2023 at 08:40:15AM +0100, David Howells wrote:
> Hi Jens, Al, Christoph,
> 
> The first half of this patchset kills off ITER_PIPE to avoid a race between
> truncate, iov_iter_revert() on the pipe and an as-yet incomplete DMA to a
> bio with unpinned/unref'ed pages from an O_DIRECT splice read.  This causes
> memory corruption[2].  Instead, we use filemap_splice_read(), which invokes
> the buffered file reading code and splices from the pagecache into the
> pipe; direct_splice_read(), which bulk-allocates a buffer, reads into it
> and then pushes the filled pages into the pipe; or handle it in
> filesystem-specific code.

If there's a clearly separate first and second half of a 32 patch
series, it might really make sense to just split it instead of exceeding
every normal attention window..