[v13,00/12] iov_iter: Improve page extraction (pin or just list)

Message

David Howells Feb. 9, 2023, 10:29 a.m. UTC

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 no longer use ITER_PIPE for doing
     a read from an O_DIRECT file fd, but rather 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) Change generic_file_splice_read() to no longer use ITER_PIPE for doing
     a read from a buffered file fd, but rather get pages directly from the
     pagecache using filemap_get_pages() do all the readahead, reading,
     waiting and extraction, and then feed the pages directly into the
     pipe.

 (3) filemap_get_pages() is altered so that it doesn't take an iterator
     (which we don't have in (2)), but rather the count and a flag
     indicating if we can handle partially uptodate pages are passed in and
     down to its subsidiary functions.

 (4) Remove ITER_PIPE and its paraphernalia as generic_file_splice_read()
     was the only user.

 (5) 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.

 (6) 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.

 (7) Add a function, bio_release_page(), to release a page appropriately to
     the cleanup mode indicated by the BIO_PAGE_* flags.

 (8) Make the iter-to-bio code use iov_iter_extract_pages() to retain the
     pages appropriately and clean them up later.

 (9) 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

David

Changes:
========
ver #13)
 - Only use allocation in advance and ITER_BVEC for DIO read-splice.
 - Make buffered read-splice get pages directly from the pagecache.
 - Alter filemap_get_pages() & co. so that it doesn't need an iterator.

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/[e-mail]/ [2]
Link: https://lore.kernel.org/r/[e-mail]/ # rfc
Link: https://lore.kernel.org/r/[e-mail]/ # rfc
Link: https://lore.kernel.org/r/[e-mail]/ # rfc
Link: https://lore.kernel.org/r/[e-mail]/ # rfc
Link: https://lore.kernel.org/r/[e-mail]/ # v2
Link: https://lore.kernel.org/r/[e-mail]/ # v3
Link: https://lore.kernel.org/r/[e-mail]/ # v4
Link: https://lore.kernel.org/r/[e-mail]/ # v5
Link: https://lore.kernel.org/r/[e-mail]/ # v6
Link: https://lore.kernel.org/r/[e-mail]/ # v7
Link: https://lore.kernel.org/r/[e-mail]/ # v8
Link: https://lore.kernel.org/r/[e-mail]/ # v9
Link: https://lore.kernel.org/r/[e-mail]/ # v10
Link: https://lore.kernel.org/r/[e-mail]/ # v11
Link: https://lore.kernel.org/r/[e-mail]/ # v12

Christoph Hellwig (1):
  block: Replace BIO_NO_PAGE_REF with BIO_PAGE_REFFED with inverted
    logic

David Howells (11):
  splice: Fix O_DIRECT file read splice to avoid reversion of ITER_PIPE
  mm: Pass info, not iter, into filemap_get_pages() and unstatic it
  splice: Do splice read from a buffered file without using 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               | 245 ++++++++++++-
 include/linux/bio.h       |   5 +-
 include/linux/blk_types.h |   3 +-
 include/linux/pagemap.h   |   2 +
 include/linux/uio.h       |  49 ++-
 lib/iov_iter.c            | 713 +++++++++++++++-----------------------
 mm/filemap.c              |  30 +-
 13 files changed, 603 insertions(+), 526 deletions(-)

Comments

Jens Axboe Feb. 10, 2023, 10:31 p.m. UTC | #1

On 2/9/23 3:29?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.

[snip]

I updated the branch to v13, just as a heads-up. Still in
for-6.3/iov-extract as before.