Messages in this thread | | | Date | Tue, 14 Feb 2023 09:54:08 +0100 | From | Greg Kroah-Hartman <> | Subject | Re: [PATCH v3 5/5] shmem, overlayfs, coda, tty, proc, kernfs, random: Fix splice-read |
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On Tue, Feb 14, 2023 at 08:37:10AM +0000, David Howells wrote: > The new filemap_splice_read() has an implicit expectation via > filemap_get_pages() that ->read_folio() exists if ->readahead() doesn't > fully populate the pagecache of the file it is reading from[1], potentially > leading to a jump to NULL if this doesn't exist. > > A filesystem or driver shouldn't suffer from this if: > > - It doesn't set ->splice_read() > - It implements ->read_folio() > - It implements its own ->splice_read() > > Note that some filesystems set generic_file_splice_read() and > generic_file_read_iter() but don't set ->read_folio(). g_f_read_iter() > will fall back to filemap_read_iter() which looks like it should suffer > from the same issue. > > Certain drivers, can just use direct_splice_read() rather than > generic_file_splice_read() as that creates an output buffer and then just > calls their ->read_iter() function: > > - random & urandom > - tty > - kernfs > - proc > - proc_namespace > > Stacked filesystems just need to pass the operation down a layer: > > - coda > - overlayfs > > And finally, there's shmem (used in tmpfs, ramfs, rootfs). This needs its > own splice-read implementation, based on filemap_splice_read(), but able to > paste in zero_page when there's a page missing. > > Fixes: d9722a475711 ("splice: Do splice read from a buffered file without using ITER_PIPE") > Signed-off-by: David Howells <dhowells@redhat.com> > cc: Daniel Golle <daniel@makrotopia.org> > cc: Guenter Roeck <groeck7@gmail.com> > cc: Christoph Hellwig <hch@lst.de> > cc: Jens Axboe <axboe@kernel.dk> > cc: Al Viro <viro@zeniv.linux.org.uk> > cc: John Hubbard <jhubbard@nvidia.com> > cc: David Hildenbrand <david@redhat.com> > cc: Matthew Wilcox <willy@infradead.org> > cc: Miklos Szeredi <miklos@szeredi.hu> > cc: Hugh Dickins <hughd@google.com> > cc: Jan Harkes <jaharkes@cs.cmu.edu> > cc: Arnd Bergmann <arnd@arndb.de> > cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > cc: coda@cs.cmu.edu > cc: codalist@coda.cs.cmu.edu > cc: linux-unionfs@vger.kernel.org > cc: linux-block@vger.kernel.org > cc: linux-fsdevel@vger.kernel.org > cc: linux-mm@kvack.org > Link: https://lore.kernel.org/r/Y+pdHFFTk1TTEBsO@makrotopia.org/ [1] > ---
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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