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@xxxxxxxxxx> > cc: Daniel Golle <daniel@xxxxxxxxxxxxxx> > cc: Guenter Roeck <groeck7@xxxxxxxxx> > cc: Christoph Hellwig <hch@xxxxxx> > cc: Jens Axboe <axboe@xxxxxxxxx> > cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> > cc: John Hubbard <jhubbard@xxxxxxxxxx> > cc: David Hildenbrand <david@xxxxxxxxxx> > cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> > cc: Miklos Szeredi <miklos@xxxxxxxxxx> > cc: Hugh Dickins <hughd@xxxxxxxxxx> > cc: Jan Harkes <jaharkes@xxxxxxxxxx> > cc: Arnd Bergmann <arnd@xxxxxxxx> > cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > cc: coda@xxxxxxxxxx > cc: codalist@xxxxxxxxxxxxxxx > cc: linux-unionfs@xxxxxxxxxxxxxxx > cc: linux-block@xxxxxxxxxxxxxxx > cc: linux-fsdevel@xxxxxxxxxxxxxxx > cc: linux-mm@xxxxxxxxx > Link: https://lore.kernel.org/r/Y+pdHFFTk1TTEBsO@xxxxxxxxxxxxxx/ [1] > --- Acked-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>