[GIT PULL] iov_iter: Improve page extraction (pin or just list)

David Howells
2023-01-30T11:14:22Z

Hi Jens,

Could you consider pulling this patchset into the block tree? I think that
Al's fears wrt to pinned pages being removed from page tables causing deadlock
have been answered. Granted, there is still the issue of how to handle
vmsplice and a bunch of other places to fix, not least skbuff handling.

I also have patches to fix cifs in a separate branch that I would also like to
push in this merge window - and that requires the first two patches from this
series also, so would it be possible for you to merge at least those two
rather than manually applying them?

Thanks,
David
-~-
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) 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.

(2) 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.

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

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

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

Changes:
========
ver #12) (unposted)
- Added the missing __bitwise on the iov_iter_extraction_t typedef.

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/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

---
The following changes since commit 2241ab53cbb5cdb08a6b2d4688feb13971058f65:

Linux 6.2-rc5 (2023-01-21 16:27:01 -0800)

are available in the Git repository at:

git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git tags/iov-extract-20230130

for you to fetch changes up to fd20d0c1852ebb3f37ec7101feb0cdd8695f32a5:

block: convert bio_map_user_iov to use iov_iter_extract_pages (2023-01-27 22:13:21 +0000)

----------------------------------------------------------------
Make block-bio use pinning

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

David Howells (7):
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/direct-io.c | 2 +
fs/iomap/direct-io.c | 1 -
include/linux/bio.h | 5 +-
include/linux/blk_types.h | 3 +-
include/linux/uio.h | 35 ++++-
lib/iov_iter.c | 335 +++++++++++++++++++++++++++++++++++++++++++++-
9 files changed, 411 insertions(+), 41 deletions(-)