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From: Al Viro <viro@ZenIV.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Dave Chinner <david@fromorbit.com>, CAI Qian <caiqian@redhat.com>,
	linux-xfs <linux-xfs@vger.kernel.org>,
	xfs@oss.sgi.com, Jens Axboe <axboe@kernel.dk>,
	Nick Piggin <npiggin@gmail.com>,
	linux-fsdevel@vger.kernel.org
Subject: [RFC][CFT] splice_read reworked
Date: Fri, 23 Sep 2016 20:00:32 +0100
Message-ID: <20160923190032.GA25771@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20160917190023.GA8039@ZenIV.linux.org.uk>

	The series is supposed to solve the locking order problems for
->splice_read() and get rid of code duplication between the read-side
methods.
	pipe_lock is lifted out of ->splice_read() instances, along with
waiting for empty space in pipe, etc. - we do that stuff in callers.
	A new variant of iov_iter is introduced - it's backed by a pipe,
copy_to_iter() results in allocating pages and copying into those,
copy_page_to_iter() just sticks a reference to that page into pipe.
Running out of space in pipe yields a short read, as a fault in iovec-backed
iov_iter would have.  Enough primitives are implemented for normal
->read_iter() instances to work.
	generic_file_splice_read() switched to feeding such iov_iter to
->read_iter() instance.  That turns out to be enough to kill almost all
->splice_read() instances; the only ones _not_ using generic_file_splice_read()
or default_file_splice_read() (== no zero-copy fallback) are
fuse_dev_splice_read(), 3 instances in kernel/{relay.c,trace/trace.c} and
sock_splice_read().  It's almost certainly possible to convert fuse one
and the same might be possible to do to socket one.  relay and tracing
stuff is just plain weird; might or might not be doable.

	Something hopefully working is in
git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git #work.splice_read

Several commits in that pipe (#1, #8 and #9) are trivial cleanups and fixes
for crap caught while doing the rest, probably ought to be separated.

Shortlog:
Al Viro (11):
      fix memory leaks in tracing_buffers_splice_read()
      splice_to_pipe(): don't open-code wakeup_pipe_readers()
      splice: switch get_iovec_page_array() to iov_iter
      splice: lift pipe_lock out of splice_to_pipe()
      skb_splice_bits(): get rid of callback
      new helper: add_to_pipe()
      fuse_dev_splice_read(): switch to add_to_pipe()
      cifs: don't use memcpy() to copy struct iov_iter
      fuse_ioctl_copy_user(): don't open-code copy_page_{to,from}_iter()
      new iov_iter flavour: pipe-backed
      switch generic_file_splice_read() to use of ->read_iter()

Diffstat:
 drivers/staging/lustre/lustre/llite/file.c         |  70 +--
 .../staging/lustre/lustre/llite/llite_internal.h   |  15 +-
 drivers/staging/lustre/lustre/llite/vvp_internal.h |  14 -
 drivers/staging/lustre/lustre/llite/vvp_io.c       |  45 +-
 fs/cifs/file.c                                     |  14 +-
 fs/coda/file.c                                     |  23 +-
 fs/fuse/dev.c                                      |  48 +-
 fs/fuse/file.c                                     |  30 +-
 fs/gfs2/file.c                                     |  28 +-
 fs/nfs/file.c                                      |  25 +-
 fs/nfs/internal.h                                  |   2 -
 fs/nfs/nfs4file.c                                  |   2 +-
 fs/ocfs2/file.c                                    |  34 +-
 fs/ocfs2/ocfs2_trace.h                             |   2 -
 fs/splice.c                                        | 578 +++++++--------------
 fs/xfs/xfs_file.c                                  |  41 +-
 fs/xfs/xfs_trace.h                                 |   1 -
 include/linux/fs.h                                 |   2 -
 include/linux/skbuff.h                             |   8 +-
 include/linux/splice.h                             |   3 +
 include/linux/uio.h                                |  14 +-
 kernel/trace/trace.c                               |  14 +-
 lib/iov_iter.c                                     | 390 +++++++++++++-
 mm/shmem.c                                         | 115 +---
 net/core/skbuff.c                                  |  28 +-
 net/ipv4/tcp.c                                     |   3 +-
 net/kcm/kcmsock.c                                  |  16 +-
 net/unix/af_unix.c                                 |  17 +-
 28 files changed, 648 insertions(+), 934 deletions(-)

	It's not all I would like to do there (in particular, I hadn't
done fuse splice_read conversion to read_iter, even though it does appear
to be doable; that'll take copy_page_to_iter_nosteal() as a new primitive
+ considerable amount of massage in fs/fuse/dev.c), but it should at least
	* make pipe lock the outermost
	* switch generic_file_splice_read() to ->read_iter(), making
it suitable for lustre/coda/gfs2/ocfs2/xfs/shmem without any wrappers
	* somewhat simplify socket ->splice_read() guts (not by much - to
start doing that right we'd need the same new primitive)
	* remove a considerable pile of code.
	* get rid of a bunch of splice_{grow,shrink}_spd/splice_to_pipe
callers; remaining ones are in default_file_splice_read() (trivially
killable by conversion to iov_iter_get_pages_alloc(), followed by the same
build iovec array + use kernel_readv as we do now + iov_iter_advance to
the length returned by kernel_readv), kernel/relay and kernel/trace/trace.c
ones (should switch to add_to_pipe(), AFAICS) and skb_splice_bits()
(again, a matter of copy_page_to_iter_nosteal(), which will take out
spd_can_coalesce/spd_fill_page in there as well).  Once the remaining ones
are taken care of, splice_pipe_desc and friends will go away.

	In its current form it survives LTP, xfstests and overlayfs testsuite;
if anybody has additional tests for splice and friends, I would like to hear
about such.  It really needs more beating, though.

	Please, help with review and testing.

  parent reply index

Thread overview: 101+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20160908235521.GL2356@ZenIV.linux.org.uk>
     [not found] ` <20160909015324.GD30056@dastard>
     [not found]   ` <CA+55aFzohsUXj_3BeFNr2t50Wm=G+7toRDEz=Tk7VJqP3n1hXQ@mail.gmail.com>
     [not found]     ` <CA+55aFxrqCng2Qxasc9pyMrKUGFjo==fEaFT1vkH9Lncte3RgQ@mail.gmail.com>
     [not found]       ` <20160909023452.GO2356@ZenIV.linux.org.uk>
     [not found]         ` <CA+55aFwHQMjO4-vtfB9-ytc=o+DRo-HXVGckvXLboUxgpwb7_g@mail.gmail.com>
     [not found]           ` <20160909221945.GQ2356@ZenIV.linux.org.uk>
     [not found]             ` <CA+55aFzTOOB6oEVaaGD0N7Uznk-W9+ULPwzsxS_L_oZqGVSeLA@mail.gmail.com>
     [not found]               ` <20160914031648.GB2356@ZenIV.linux.org.uk>
     [not found]                 ` <20160914133925.2fba4629@roar.ozlabs.ibm.com>
2016-09-18  5:33                   ` xfs_file_splice_read: possible circular locking dependency detected Al Viro
2016-09-19  3:08                     ` Nicholas Piggin
2016-09-19  6:11                       ` Al Viro
2016-09-19  7:26                         ` Nicholas Piggin
     [not found]                 ` <CA+55aFznQaOWoSMNphgGJJWZ=8-odrc0DAUMzfGPQe+_N4UgNA@mail.gmail.com>
     [not found]                   ` <20160914042559.GC2356@ZenIV.linux.org.uk>
     [not found]                     ` <20160917082007.GA6489@ZenIV.linux.org.uk>
     [not found]                       ` <20160917190023.GA8039@ZenIV.linux.org.uk>
2016-09-18 19:31                         ` skb_splice_bits() and large chunks in pipe (was " Al Viro
2016-09-18 20:12                           ` Linus Torvalds
2016-09-18 22:31                             ` Al Viro
2016-09-19  0:18                               ` Linus Torvalds
2016-09-23 19:00                         ` Al Viro [this message]
2016-09-23 19:01                           ` [PATCH 01/11] fix memory leaks in tracing_buffers_splice_read() Al Viro
2016-09-23 19:02                           ` [PATCH 02/11] splice_to_pipe(): don't open-code wakeup_pipe_readers() Al Viro
2016-09-23 19:02                           ` [PATCH 03/11] splice: switch get_iovec_page_array() to iov_iter Al Viro
2016-09-23 19:03                           ` [PATCH 04/11] splice: lift pipe_lock out of splice_to_pipe() Al Viro
2016-09-23 19:45                             ` Linus Torvalds
2016-09-23 20:10                               ` Al Viro
2016-09-23 20:36                                 ` Linus Torvalds
2016-09-24  3:59                                   ` Al Viro
2016-09-24 17:29                                     ` Al Viro
2016-09-27 15:38                                       ` Nicholas Piggin
2016-09-27 15:53                                       ` Chuck Lever
2016-09-24  3:59                                   ` [PATCH 04/12] " Al Viro
2016-09-26 13:35                                     ` Miklos Szeredi
2016-09-27  4:14                                       ` Al Viro
2016-12-17 19:54                                     ` Andreas Schwab
2016-12-18 19:28                                       ` Linus Torvalds
2016-12-18 19:57                                         ` Andreas Schwab
2016-12-18 20:12                                         ` Al Viro
2016-12-18 20:30                                           ` Al Viro
2016-12-18 22:10                                             ` Linus Torvalds
2016-12-18 22:18                                               ` Al Viro
2016-12-18 22:22                                                 ` Linus Torvalds
2016-12-18 22:49                                               ` Andreas Schwab
2016-12-21 18:56                                               ` Andreas Schwab
2016-12-21 19:12                                                 ` Linus Torvalds
2016-09-24  4:00                                   ` [PATCH 06/12] new helper: add_to_pipe() Al Viro
2016-09-26 13:49                                     ` Miklos Szeredi
2016-09-24  4:01                                   ` [PATCH 10/12] new iov_iter flavour: pipe-backed Al Viro
2016-09-29 20:53                                     ` Miklos Szeredi
2016-09-29 22:50                                       ` Al Viro
2016-09-30  7:30                                         ` Miklos Szeredi
2016-10-03  3:34                                           ` [RFC] O_DIRECT vs EFAULT (was Re: [PATCH 10/12] new iov_iter flavour: pipe-backed) Al Viro
2016-10-03 17:07                                             ` Linus Torvalds
2016-10-03 18:54                                               ` Al Viro
2016-09-24  4:01                                   ` [PATCH 11/12] switch generic_file_splice_read() to use of ->read_iter() Al Viro
2016-09-24  4:02                                   ` [PATCH 12/12] switch default_file_splice_read() to use of pipe-backed iov_iter Al Viro
2016-09-23 19:03                           ` [PATCH 05/11] skb_splice_bits(): get rid of callback Al Viro
2016-09-23 19:04                           ` [PATCH 06/11] new helper: add_to_pipe() Al Viro
2016-09-23 19:04                           ` [PATCH 07/11] fuse_dev_splice_read(): switch to add_to_pipe() Al Viro
2016-09-23 19:06                           ` [PATCH 08/11] cifs: don't use memcpy() to copy struct iov_iter Al Viro
2016-09-23 19:08                           ` [PATCH 09/11] fuse_ioctl_copy_user(): don't open-code copy_page_{to,from}_iter() Al Viro
2016-09-26  9:31                             ` Miklos Szeredi
2016-09-23 19:09                           ` [PATCH 10/11] new iov_iter flavour: pipe-backed Al Viro
2016-09-23 19:10                           ` [PATCH 11/11] switch generic_file_splice_read() to use of ->read_iter() Al Viro
2016-09-30 13:32                           ` [RFC][CFT] splice_read reworked CAI Qian
2016-09-30 17:42                             ` CAI Qian
2016-09-30 18:33                               ` CAI Qian
2016-10-03  1:37                                 ` Al Viro
2016-10-03 17:49                                   ` CAI Qian
2016-10-04 17:39                                     ` local DoS - systemd hang or timeout (WAS: Re: [RFC][CFT] splice_read reworked) CAI Qian
2016-10-04 21:42                                       ` tj
2016-10-05 14:09                                         ` CAI Qian
2016-10-05 15:30                                           ` tj
2016-10-05 15:54                                             ` CAI Qian
2016-10-05 18:57                                               ` CAI Qian
2016-10-05 20:05                                                 ` Al Viro
2016-10-06 12:20                                                   ` CAI Qian
2016-10-06 12:25                                                     ` CAI Qian
2016-10-06 16:11                                                       ` CAI Qian
2016-10-06 17:00                                                         ` Linus Torvalds
2016-10-06 18:12                                                           ` CAI Qian
2016-10-07  9:57                                                           ` Dave Chinner
2016-10-07 15:25                                                             ` Linus Torvalds
2016-10-07  7:08                                                       ` Jan Kara
2016-10-07 14:43                                                         ` CAI Qian
2016-10-07 15:27                                                           ` CAI Qian
2016-10-07 18:56                                                             ` CAI Qian
2016-10-09 21:54                                                               ` Dave Chinner
2016-10-10 14:10                                                                 ` CAI Qian
2016-10-10 20:14                                                                   ` CAI Qian
2016-10-10 21:57                                                                   ` Dave Chinner
2016-10-12 19:50                                                                     ` [bisected] " CAI Qian
2016-10-12 20:59                                                                       ` Dave Chinner
2016-10-13 16:25                                                                         ` CAI Qian
2016-10-13 20:49                                                                           ` Dave Chinner
2016-10-13 20:56                                                                             ` CAI Qian
2016-10-09 21:51                                                           ` Dave Chinner
2016-10-21 15:38                                                         ` [4.9-rc1+] overlayfs lockdep CAI Qian
2016-10-24 12:57                                                           ` Miklos Szeredi
2016-10-07  9:27                                                     ` local DoS - systemd hang or timeout (WAS: Re: [RFC][CFT] splice_read reworked) Dave Chinner
2016-10-03  1:42                               ` [RFC][CFT] splice_read reworked Al Viro
2016-10-03 14:06                                 ` CAI Qian
2016-10-03 15:20                                   ` CAI Qian
2016-10-03 21:12                                     ` Dave Chinner
2016-10-04 13:57                                       ` CAI Qian
2016-10-03 20:32                                   ` CAI Qian
2016-10-03 20:35                                     ` Al Viro
2016-10-04 13:29                                       ` CAI Qian
2016-10-04 14:28                                         ` Al Viro
2016-10-04 16:21                                           ` CAI Qian
2016-10-04 20:12                                             ` Al Viro
2016-10-05 14:30                                               ` CAI Qian
2016-10-05 16:07                                                 ` Al Viro
2016-09-19  0:22 skb_splice_bits() and large chunks in pipe (was Re: xfs_file_splice_read: possible circular locking dependency detected Al Viro
2016-09-20  9:51 ` Herbert Xu

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