[PATCH v14 00/17] iov_iter: Improve page extraction (pin or just list)

David Howells
2023-02-14T17:14:45Z

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(-)