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Date: Sun, 28 Aug 2022 01:38:56 +0100 From: Al Viro <viro@...iv.linux.org.uk> To: John Hubbard <jhubbard@...dia.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, Jens Axboe <axboe@...nel.dk>, Miklos Szeredi <miklos@...redi.hu>, Christoph Hellwig <hch@...radead.org>, "Darrick J . Wong" <djwong@...nel.org>, Trond Myklebust <trond.myklebust@...merspace.com>, Anna Schumaker <anna@...nel.org>, Jan Kara <jack@...e.cz>, Logan Gunthorpe <logang@...tatee.com>, linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-xfs@...r.kernel.org, linux-nfs@...r.kernel.org, linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 5/6] NFS: direct-io: convert to FOLL_PIN pages On Sat, Aug 27, 2022 at 04:55:18PM -0700, John Hubbard wrote: > On 8/27/22 15:48, Al Viro wrote: > > On Sat, Aug 27, 2022 at 01:36:06AM -0700, John Hubbard wrote: > >> Convert the NFS Direct IO layer to use pin_user_pages_fast() and > >> unpin_user_page(), instead of get_user_pages_fast() and put_page(). > > > > Again, this stuff can be hit with ITER_BVEC iterators > > > >> - result = iov_iter_get_pages_alloc2(iter, &pagevec, > >> + result = dio_w_iov_iter_pin_pages_alloc(iter, &pagevec, > >> rsize, &pgbase); > > > > and this will break on those. > > If anyone has an example handy, of a user space program that leads > to this situation (O_DIRECT with ITER_BVEC), it would really help > me reach enlightenment a lot quicker in this area. :) Er... splice(2) to O_DIRECT-opened file on e.g. ext4? Or sendfile(2) to the same, for that matter...
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