| Message ID | 20230207171305.3716974-1-dhowells@redhat.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | iov_iter: Improve page extraction (pin or just list) | expand |
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 <axboe@kernel.dk> wrote: > 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). Thanks! David
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 pushed the patches here also: https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=iov-extract and tagged it with iov-extract-20230207 David Changes: ======== ver #12) - Added the missing __bitwise on the iov_iter_extraction_t typedef. - Rebased on -rc7. - Don't specify FOLL_PIN to pin_user_pages_fast(). - Inserted patch at front to fix race between DIO read and truncation that caused memory corruption when iov_iter_revert() got called on an ITER_PIPE iterator[2]. - Inserted a patch after that to remove the now-unused ITER_PIPE and its helper functions. - Removed the ITER_PIPE bits from iov_iter_extract_pages(). ver #11) - Fix iov_iter_extract_kvec_pages() to include the offset into the page in the returned starting offset. - Use __bitwise for the extraction flags ver #10) - Fix use of i->kvec in iov_iter_extract_bvec_pages() to be i->bvec. - Drop bio_set_cleanup_mode(), open coding it instead. ver #9) - It's now not permitted to use FOLL_PIN outside of mm/, so: - Change iov_iter_extract_mode() into iov_iter_extract_will_pin() and return true/false instead of FOLL_PIN/0. - Drop of folio_put_unpin() and page_put_unpin() and instead call unpin_user_page() (and put_page()) directly as necessary. - Make __bio_release_pages() call bio_release_page() instead of unpin_user_page() as there's no BIO_* -> FOLL_* translation to do. - Drop the FOLL_* renumbering patch. - Change extract_flags to extraction_flags. ver #8) - Import Christoph Hellwig's changes. - Split the conversion-to-extraction patch. - Drop the extract_flags arg from iov_iter_extract_mode(). - Don't default bios to BIO_PAGE_REFFED, but set explicitly. - Switch FOLL_PIN and FOLL_GET when renumbering so PIN is at bit 0. - Switch BIO_PAGE_PINNED and BIO_PAGE_REFFED so PINNED is at bit 0. - We should always be using FOLL_PIN (not FOLL_GET) for DIO, so adjust the patches for that. ver #7) - For now, drop the parts to pass the I/O direction to iov_iter_*pages*() as it turned out to be a lot more complicated, with places not setting IOCB_WRITE when they should, for example. - Drop all the patches that changed things other then the block layer's bio handling. The netfslib and cifs changes can go into a separate patchset. - Add support for extracting pages from KVEC-type iterators. - When extracting from BVEC/KVEC, skip over empty vecs at the front. ver #6) - Fix write() syscall and co. not setting IOCB_WRITE. - Added iocb_is_read() and iocb_is_write() to check IOCB_WRITE. - Use op_is_write() in bio_copy_user_iov(). - Drop the iterator direction checks from smbd_recv(). - Define FOLL_SOURCE_BUF and FOLL_DEST_BUF and pass them in as part of gup_flags to iov_iter_get/extract_pages*(). - Replace iov_iter_get_pages*2() with iov_iter_get_pages*() and remove. - Add back the function to indicate the cleanup mode. - Drop the cleanup_mode return arg to iov_iter_extract_pages(). - Provide a helper to clean up a page. - Renumbered FOLL_GET and FOLL_PIN and made BIO_PAGE_REFFED/PINNED have the same numerical values, enforced with an assertion. - Converted AF_ALG, SCSI vhost, generic DIO, FUSE, splice to pipe, 9P and NFS. - Added in the patches to make CIFS do top-to-bottom iterators and use various of the added extraction functions. - Added a pair of work-in-progess patches to make sk_buff fragments store FOLL_GET and FOLL_PIN. ver #5) - Replace BIO_NO_PAGE_REF with BIO_PAGE_REFFED and split into own patch. - Transcribe FOLL_GET/PIN into BIO_PAGE_REFFED/PINNED flags. - Add patch to allow bio_flagged() to be combined by gcc. ver #4) - Drop the patch to move the FOLL_* flags to linux/mm_types.h as they're no longer referenced by linux/uio.h. - Add ITER_SOURCE/DEST cleanup patches. - Make iov_iter/netfslib iter extraction patches use ITER_SOURCE/DEST. - Allow additional gup_flags to be passed into iov_iter_extract_pages(). - Add struct bio patch. ver #3) - Switch to using EXPORT_SYMBOL_GPL to prevent indirect 3rd-party access to get/pin_user_pages_fast()[1]. ver #2) - Rolled the extraction cleanup mode query function into the extraction function, returning the indication through the argument list. - Fixed patch 4 (extract to scatterlist) to actually use the new extraction API. Link: https://lore.kernel.org/r/Y3zFzdWnWlEJ8X8/@infradead.org/ [1] Link: https://lore.kernel.org/r/000000000000b0b3c005f3a09383@google.com/ [2] Link: https://lore.kernel.org/r/166697254399.61150.1256557652599252121.stgit@warthog.procyon.org.uk/ # rfc Link: https://lore.kernel.org/r/166722777223.2555743.162508599131141451.stgit@warthog.procyon.org.uk/ # rfc Link: https://lore.kernel.org/r/166732024173.3186319.18204305072070871546.stgit@warthog.procyon.org.uk/ # rfc Link: https://lore.kernel.org/r/166869687556.3723671.10061142538708346995.stgit@warthog.procyon.org.uk/ # rfc Link: https://lore.kernel.org/r/166920902005.1461876.2786264600108839814.stgit@warthog.procyon.org.uk/ # v2 Link: https://lore.kernel.org/r/166997419665.9475.15014699817597102032.stgit@warthog.procyon.org.uk/ # v3 Link: https://lore.kernel.org/r/167305160937.1521586.133299343565358971.stgit@warthog.procyon.org.uk/ # v4 Link: https://lore.kernel.org/r/167344725490.2425628.13771289553670112965.stgit@warthog.procyon.org.uk/ # v5 Link: https://lore.kernel.org/r/167391047703.2311931.8115712773222260073.stgit@warthog.procyon.org.uk/ # v6 Link: https://lore.kernel.org/r/20230120175556.3556978-1-dhowells@redhat.com/ # v7 Link: https://lore.kernel.org/r/20230123173007.325544-1-dhowells@redhat.com/ # v8 Link: https://lore.kernel.org/r/20230124170108.1070389-1-dhowells@redhat.com/ # v9 Link: https://lore.kernel.org/r/20230125210657.2335748-1-dhowells@redhat.com/ # v10 Link: https://lore.kernel.org/r/20230126141626.2809643-1-dhowells@redhat.com/ # v11 Christoph Hellwig (1): block: Replace BIO_NO_PAGE_REF with BIO_PAGE_REFFED with inverted logic David Howells (9): vfs, iomap: Fix generic_file_splice_read() to avoid reversion of ITER_PIPE iov_iter: Kill ITER_PIPE iov_iter: Define flags to qualify page extraction. iov_iter: Add a function to extract a page list from an iterator iomap: Don't get an reference on ZERO_PAGE for direct I/O block zeroing block: Fix bio_flagged() so that gcc can better optimise it block: Add BIO_PAGE_PINNED and associated infrastructure block: Convert bio_iov_iter_get_pages to use iov_iter_extract_pages block: convert bio_map_user_iov to use iov_iter_extract_pages block/bio.c | 33 +- block/blk-map.c | 26 +- block/blk.h | 12 + fs/cifs/file.c | 8 +- fs/direct-io.c | 2 + fs/iomap/direct-io.c | 1 - fs/splice.c | 76 +++- include/linux/bio.h | 5 +- include/linux/blk_types.h | 3 +- include/linux/uio.h | 49 ++- lib/iov_iter.c | 713 +++++++++++++++----------------------- mm/filemap.c | 3 - 12 files changed, 426 insertions(+), 505 deletions(-)