On 2/7/23 10:12 AM, David Howells wrote: > Hi Jens, Al, Christoph, > > Here are patches to provide support for extracting pages from an iov_iter > and to use this in the extraction functions in the block layer bio code. > > The patches make the following changes: > > (1) Change generic_file_splice_read() to load up an ITER_BVEC iterator > with sufficient pages and use that rather than using an ITER_PIPE. > This avoids a problem[2] when __iomap_dio_rw() calls iov_iter_revert() > to shorten an iterator when it races with truncation. The reversion > causes the pipe iterator to prematurely release the pages it was > retaining - despite the read still being in progress. This caused > memory corruption. > > (2) Remove ITER_PIPE and its paraphernalia as generic_file_splice_read() > was the only user. > > (3) Add a function, iov_iter_extract_pages() to replace > iov_iter_get_pages*() that gets refs, pins or just lists the pages as > appropriate to the iterator type. > > Add a function, iov_iter_extract_will_pin() that will indicate from > the iterator type how the cleanup is to be performed, returning true > if the pages will need unpinning, false otherwise. > > (4) Make the bio struct carry a pair of flags to indicate the cleanup > mode. BIO_NO_PAGE_REF is replaced with BIO_PAGE_REFFED (indicating > FOLL_GET was used) and BIO_PAGE_PINNED (indicating FOLL_PIN was used) > is added. > > BIO_PAGE_REFFED will go away, but at the moment fs/direct-io.c sets it > and this series does not fully address that file. > > (5) Add a function, bio_release_page(), to release a page appropriately to > the cleanup mode indicated by the BIO_PAGE_* flags. > > (6) Make the iter-to-bio code use iov_iter_extract_pages() to retain the > pages appropriately and clean them up later. > > (7) Fix bio_flagged() so that it doesn't prevent a gcc optimisation. I've updated the for-6.3/iov-extract branch and the for-next branch. This isn't done to bypass any review, just so we can get some more testing on this (and because the old one is known broken). -- Jens Axboe
