[PATCH 00/17] smb3: Use iov_iters down to the network transport and fix DIO page pinning

David Howells
2023-02-16T21:48:51Z

Hi Steve,

Here's an updated version of my patchset to make the cifs/smb3 driver pass
iov_iters down to the lowest layers where they can be passed directly to
the network transport rather than passing lists of pages around.

The series deals with the following issues:

(-) By pinning pages, it fixes the race between concurrent DIO read and
fork, whereby the pages containing the DIO read buffer may end up
belonging to the child process and not the parent - with the result
that the parent might not see the retrieved data.

(-) cifs shouldn't take refs on pages extracted from non-user-backed
iterators (eg. KVEC). With these changes, cifs will apply the
appropriate cleanup. Note that there is the possibility the network
transport might, but that's beyond the scope of this patchset.

(-) Making it easier to transition to using folios in cifs rather than
pages by dealing with them through BVEC and XARRAY iterators.

The first five patches add two facilities to the VM/VFS core, excerpts from
my iov-extract branch[1] that are required in order to do the cifs
iteratorisation:

(*) Future replacements for file-splicing in the form of functions
filemap_splice_read() and direct_splice_read(). These allow file
splicing to be done without the use of an ITER_PIPE iterator, without
the need to take refs on the pages extracted from KVEC/BVEC/XARRAY
iterators. This is necessary to use iov_iter_extract_pages().

[!] Note that whilst these are added in core code, they are only used
by cifs at this point.

(*) Add iov_iter_extract_pages(), a replacement for iov_iter_get_pages*()
that uses FOLL_PIN on user pages (IOVEC, UBUF) and doesn't pin kernel
pages (BVEC, KVEC, XARRAY). This allows cifs to do the page pinning
correctly.

[!] Note that whilst this is added in core code, it is only used by
cifs at this point - though a corresponding change is made to the
flags argument of iov_iter_get_pages*() so that it doesn't take FOLL_*
flags, but rather takes iov_iter_extraction_t flags that are
translated internally to FOLL_* flags.

Then there's a couple of patches to make cifs use the new splice functions.

The series continues with a couple of patches that add stuff to netfslib
that I want to use there as well as in cifs:

(*) Add a netfslib function to extract and pin pages from an ITER_IOBUF or
ITER_UBUF iterator into an ITER_BVEC iterator.

(*) Add a netfslib function to extract pages from an iterator that's of
type ITER_UBUF/IOVEC/BVEC/KVEC/XARRAY and add them to a scatterlist.
The cleanup will need to be done as for iov_iter_extract_pages().

BVEC, KVEC and XARRAY iterators can be rendered into elements that
span multiple pages.

Added to that are some cifs helpers that work with iterators:

(*) Add a function to walk through an ITER_BVEC/KVEC/XARRAY iterator and
add elements to an RDMA SGE list. Only the DMA addresses are stored,
and an element may span multiple pages (say if an xarray contains a
multipage folio).

(*) Add a function to walk through an ITER_BVEC/KVEC/XARRAY iterator and
pass the contents into a shash function.

(*) Add functions to walk through an ITER_XARRAY iterator and perform
various sorts of cleanup on the folios held therein, to be used on I/O
completion.

(*) Add a function to read from the transport TCP socket directly into an
iterator.

Finally come the patches that actually do the work of iteratorising cifs:

(*) The main patch. Replace page lists with iterators. It extracts the
pages from ITER_UBUF and ITER_IOVEC iterators to an ITER_BVEC
iterator, pinning or getting refs on them, before passing them down as
the I/O may be done from a worker thread.

The iterator is extracted into a scatterlist in order to talk to the
crypto interface or to do RDMA.

(*) In the cifs RDMA code, extract the iterator into an RDMA SGE[] list,
removing the scatterlist intermediate - at least for smbd_send().
There appear to be other ways for cifs to talk to the RDMA layer that
don't go through that that I haven't managed to work out.

(*) Remove a chunk of now-unused code.

(*) Allow DIO to/from KVEC-type iterators.

I've pushed the patches here also:

https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=iov-cifs

David

Link: https://lore.kernel.org/r/20230214171330.2722188-1-dhowells@redhat.com/ [1]
Link: https://lore.kernel.org/r/166697254399.61150.1256557652599252121.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/20230131182855.4027499-1-dhowells@redhat.com/ # v1

David Howells (17):
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
iov_iter: Define flags to qualify page extraction.
iov_iter: Add a function to extract a page list from an iterator
splice: Export filemap/direct_splice_read()
cifs: Implement splice_read to pass down ITER_BVEC not ITER_PIPE
netfs: Add a function to extract a UBUF or IOVEC into a BVEC iterator
netfs: Add a function to extract an iterator into a scatterlist
cifs: Add a function to build an RDMA SGE list from an iterator
cifs: Add a function to Hash the contents of an iterator
cifs: Add some helper functions
cifs: Add a function to read into an iter from a socket
cifs: Change the I/O paths to use an iterator rather than a page list
cifs: Build the RDMA SGE list directly from an iterator
cifs: Remove unused code
cifs: DIO to/from KVEC-type iterators should now work

block/bio.c | 6 +-
block/blk-map.c | 8 +-
fs/cifs/Kconfig | 1 +
fs/cifs/cifsencrypt.c | 172 +++-
fs/cifs/cifsfs.c | 12 +-
fs/cifs/cifsfs.h | 6 +
fs/cifs/cifsglob.h | 66 +-
fs/cifs/cifsproto.h | 11 +-
fs/cifs/cifssmb.c | 15 +-
fs/cifs/connect.c | 14 +
fs/cifs/file.c | 1772 ++++++++++++++++---------------------
fs/cifs/fscache.c | 22 +-
fs/cifs/fscache.h | 10 +-
fs/cifs/misc.c | 128 +--
fs/cifs/smb2ops.c | 362 ++++----
fs/cifs/smb2pdu.c | 53 +-
fs/cifs/smbdirect.c | 535 ++++++-----
fs/cifs/smbdirect.h | 7 +-
fs/cifs/transport.c | 54 +-
fs/netfs/Makefile | 1 +
fs/netfs/iterator.c | 371 ++++++++
fs/splice.c | 93 ++
include/linux/fs.h | 6 +
include/linux/netfs.h | 8 +
include/linux/pipe_fs_i.h | 20 +
include/linux/uio.h | 35 +-
lib/iov_iter.c | 284 +++++-
mm/filemap.c | 156 +++-
mm/internal.h | 6 +
mm/vmalloc.c | 1 +
30 files changed, 2515 insertions(+), 1720 deletions(-)
create mode 100644 fs/netfs/iterator.c