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    Subject[PATCH v14 00/17] iov_iter: Improve page extraction (pin or just list)
    Date
    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 #14)
    - Some changes to generic_file_buffered_splice_read():
    - Rename to filemap_splice_read() and move to mm/filemap.c.
    - Create a helper, pipe_head_buf().
    - Use init_sync_kiocb().
    - Some changes to generic_file_direct_splice_read():
    - Use alloc_pages_bulk_array() rather than alloc_pages_bulk_list().
    - Use release_pages() instead of __free_page() in a loop.
    - Rename to direct_splice_read().
    - Rearrange the patches to implement filemap_splice_read() and
    direct_splice_read() separately to changing generic_file_splice_read().
    - Don't call generic_file_splice_read() when there isn't a ->read_folio().
    - Insert patches to fix read_folio-less cases:
    - Make tty, procfs, kernfs and (u)random use direct_splice_read().
    - Make overlayfs and coda call down to a lower layer.
    - Give shmem its own splice-read that doesn't insert missing pages.
    - Fixed a min() with mixed type args on some arches.

    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/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
    Link: https://lore.kernel.org/r/20230207171305.3716974-1-dhowells@redhat.com/ # v12
    Link: https://lore.kernel.org/r/20230209102954.528942-1-dhowells@redhat.com/ # v13

    Additional patches that got folded in:

    Link: https://lore.kernel.org/r/20230213134619.2198965-1-dhowells@redhat.com/ # v1
    Link: https://lore.kernel.org/r/20230213153301.2338806-1-dhowells@redhat.com/ # v2
    Link: https://lore.kernel.org/r/20230214083710.2547248-1-dhowells@redhat.com/ # v3

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

    David Howells (16):
    mm: Pass info, not iter, into filemap_get_pages()
    splice: Add a func to do a splice from a buffered file without
    ITER_PIPE
    splice: Add a func to do a splice from an O_DIRECT file without
    ITER_PIPE
    shmem: Implement splice-read
    overlayfs: Implement splice-read
    coda: Implement splice-read
    tty, proc, kernfs, random: Use direct_splice_read()
    splice: Do splice read from a 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 +
    drivers/char/random.c | 4 +-
    drivers/tty/tty_io.c | 4 +-
    fs/cifs/file.c | 8 +-
    fs/coda/file.c | 36 +-
    fs/direct-io.c | 2 +
    fs/iomap/direct-io.c | 1 -
    fs/kernfs/file.c | 2 +-
    fs/overlayfs/file.c | 36 +-
    fs/proc/inode.c | 4 +-
    fs/proc/proc_sysctl.c | 2 +-
    fs/proc_namespace.c | 6 +-
    fs/splice.c | 114 +++++-
    include/linux/bio.h | 5 +-
    include/linux/blk_types.h | 3 +-
    include/linux/fs.h | 6 +
    include/linux/pipe_fs_i.h | 20 ++
    include/linux/uio.h | 49 ++-
    lib/iov_iter.c | 713 +++++++++++++++-----------------------
    mm/filemap.c | 154 +++++++-
    mm/internal.h | 6 +
    mm/shmem.c | 124 ++++++-
    24 files changed, 830 insertions(+), 540 deletions(-)

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