[PATCH v16 00/13] splice, block: Use page pinning and kill ITER_PIPE

David Howells
2023-03-08T14:38:57Z

Hi Jens, Al, Christoph,

The first half of this patchset kills off ITER_PIPE to avoid a race between
truncate, iov_iter_revert() on the pipe and an as-yet incomplete DMA to a
bio with unpinned/unref'ed pages from an O_DIRECT splice read. This causes
memory corruption[2]. Instead, we use filemap_splice_read(), which invokes
the buffered file reading code and splices from the pagecache into the
pipe; direct_splice_read(), which bulk-allocates a buffer, reads into it
and then pushes the filled pages into the pipe; or handle it in
filesystem-specific code.

(1) Simplify the calculations for the number of pages to be reclaimed in
direct_splice_read().

(2) Provide shmem with its own splice_read to handle non-existent pages
in the pagecache. We don't want a ->read_folio() as we don't want to
populate holes, but filemap_get_pages() requires it.

(3) Provide overlayfs with its own splice_read to call down to a lower
layer as overlayfs doesn't provide ->read_folio().

(4) Provide coda with its own splice_read to call down to a lower layer as
coda doesn't provide ->read_folio().

(5) Direct ->splice_read to direct_splice_read() in tty, procfs, kernfs
and random files as they just copy to the output buffer and don't
splice pages.

(6) Change generic_file_splice_read() to just switch between
filemap_splice_read() and direct_splice_read() rather than using
ITER_PIPE.

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

The second half of the patchset rolls page-pinning out to the bio struct
and the block layer, using iov_iter_extract_pages() to get pages and noting
with BIO_PAGE_PINNED if the data pages attached to a bio are pinned. If
the data pages come from a non-user-backed iterator, then the pages are
left unpinned and unref'd, relying on whoever set up the I/O to do the
retaining

(8) Don't hold a ref on ZERO_PAGE in iomap_dio_zero().

(9) Fix bio_flagged() so that it doesn't prevent a gcc optimisation.

(10) 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.

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

(12) Make bio_iov_iter_get_pages() use iov_iter_extract_pages() to retain
the pages appropriately and clean them up later.

(13) Make bio_map_user_iov() also use iov_iter_extract_pages().

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 #16)
- The filemap_get_pages() changes are now upstream.
- filemap_splice_read() and direct_splice_read() are now upstream.
- iov_iter_extract_pages() is now upstream.

ver #15)
- Fixed up some errors in overlayfs_splice_read().

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
Link: https://lore.kernel.org/r/20230214171330.2722188-1-dhowells@redhat.com/ # v14

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 (12):
splice: Clean up direct_splice_read() a bit
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
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 | 29 +--
block/blk-map.c | 22 +-
block/blk.h | 12 ++
drivers/char/random.c | 4 +-
drivers/tty/tty_io.c | 4 +-
fs/cifs/cifsfs.c | 8 +-
fs/cifs/cifsfs.h | 3 -
fs/cifs/file.c | 16 --
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 | 33 ++-
fs/proc/inode.c | 4 +-
fs/proc/proc_sysctl.c | 2 +-
fs/proc_namespace.c | 6 +-
fs/splice.c | 49 ++---
include/linux/bio.h | 5 +-
include/linux/blk_types.h | 3 +-
include/linux/uio.h | 14 --
lib/iov_iter.c | 429 +-------------------------------------
mm/filemap.c | 4 +-
mm/shmem.c | 124 ++++++++++-
23 files changed, 268 insertions(+), 544 deletions(-)